Here's what you can do.
I had a machine where I needed to install my games on a separate drive
so I symlinked the steamapps directory.
You can do the same with the directories inside of steamapps.
I've gotten it working in Vista and Windows 7 using mklink .
EDIT:
Install Steam on the SSD and then symlink the games you aren't using as much with their data on the slower drive.
gaming.stackexchange.com/users/44/Corv1nus
As of the latest Steam version for Windows, it is possible to install games to arbitrary locations.
To do so, click "Install" in your library or the store and choose "Create new Steam library" in the "Choose drive to install to" dropdown menu.
This option will only be available for games using the new content system, you may need to use the tricks from the other answers if you want to move the ones that don't use it.
Note that the Install dialogue will not offer the option to create a separate library on a drive that already has one, to do that you need to go to
Steam -> Settings ->
Downloads + Cloud -> Steam Library Folders and click on "Add library folder".
gaming.stackexchange.com/users/19827/kotekzot
There are now a couple tools that help with this process: http://stefanjones.ca/steam/ and http://www.traynier.com/software/steammover
gaming.stackexchange.com/users/1593/Shane Fulmer
There is now native support for this feature on Windows.
You'll see the option at install time.
gaming.stackexchange.com/users/23/badp
Something like this is completely possible -- one way is to simply install two separate copies of Steam, one on each drive.
Just make sure to close out of the one instance before changing to a game installed under the other (Steam won't let more than one of itself run at any time)
gaming.stackexchange.com/users/336/Raven Dreamer
As Alastair Pitts said, you can't have dual-located /steamapps folders.
However, if you're worried about space, you can collect the GCFs from the steam apps folder, and store these on a separate drive, then re-locate them when you want to play these infrequently played games.
Further, you could 'uninstall' them from your steam games, but bring them back with the gcf's when you need them; but this may involve more bandwidth consumption that indented (if steam wants to check for updates, etc)
gaming.stackexchange.com/users/159/glasnt
(Windows OS solution) Symbolic links are an excellent solution to hosting games in a location that isn't the actual install location, or on a hard drive that is not your primary drive.
They are similar to creating shortcuts, but the difference is that Windows will see them as actual paths, not shortcuts.
For example: C:\ is my primary drive.
Windows is installed on this drive.
I create a symbolic link (very similar to a shortcut) at 'C:\Battlefield' which points to 'E:\Battlefield'.
Now, I can install Battlefield to 'C:\Battlefield', and as far as Windows is concerned, that is where it is installed.
But, the files are actually kept on 'E:\Battlefield'
since that is where the symbolic link points to!
The command for this would be: mklink /D "C:\Battlefield" "E:\Battlefield"
For this command to work, the target ("E:\Battlefield") must exist, and the link ("C:\Battlefield") must not exist before the command is executed.
If you already have your application installed at the C:\ directory, you could copy it over to the E:\ directory (while it isn't running), and then delete the empty C:\ folder before executing the command.
You can execute this from windows command line.
In Windows 7, just type ' cmd ' into the search bar within the Start menu and press Enter to open the command line.
In Windows XP, go through Start menu, click ' Run ' and then enter ' cmd ' for the parameter and press Enter!
I only used the name 'E:\Battlefield'
as an example, you could name this whatever you want. '
E:\games\bf3' would work as well, or whatever other path/name
you wish to give it.
This method is extremely effective when your primary hard drive is a solid state drive without much space, but you want your installed applications to be seen on the primary drive.
Especially nice for the Steamapps folder, or specific games within it.
gaming.stackexchange.com/users/20055/Lemmings19
If you know the location where the game will be installed before installing it, I don't see anything stopping you from making a symlink to a particular game and then installing.
I'll have to give this a try to see if it works.
gaming.stackexchange.com/users/46/cowgod
No, this is not possible unfortunately.
Steam stores all* of it's games in the /steamapps subfolder in the installation directory.
*
There are some games that, for whatever reason, install themselves outside of this folder, but it's not something that you can control/decide.
gaming.stackexchange.com/users/198/Alastair Pitts
You can set up multiple steam library folders in settings (even on separate drives), then go to the game(s)
that you want on the new drive, right click in steam - settings - local files - move folder - select new library folder wait for files to transfer and ur good!
gaming.stackexchange.com/users/213822/Regnitto
I want to build a new PC with a smallish SSD.  I'd like to be able to install some of my games onto the drive (those I care about loading quickly or I play frequently), but have the rest of them on a larger, slower drive.  Anybody know if this is possible?  I'm kind of guessing it's not, but figured I'd ask anyway.
Is it possible to install Steam games to two different locations?
gaming.stackexchange.com
<steam>
gaming.stackexchange.com/questions/1580
gaming.stackexchange.com/users/297/Morinar
You can install Steam on the SSD and symlink the games you aren't using much on the slower drive. With the latest version of Steam, you can store games in different locations. You could also download two versions of Steam, one on each drive. You can install Steam on the SSD and then symlink the games you aren't using as much with their data on the slower drive.  As of the latest Steam version for Windows, it is possible to install games to arbitrary locations by clicking "Install" in your library or the store and choose "Create new Steam library" in the "Choose drive to install to" dropdown menu. There are now also a couple of tools that help with this process: http://stefanjones.ca/steam/  and http://www.traynier.com/software/steammover. There are now also a couple of tools that help with this process: http://stefanjones.ca/steam/  and http://www.traynier.com/software/steammover. There is also native support for this feature  on Windows.
You can install Steam on the SSD and then symlink the games you aren't using as much with their data on the slower drive.   As of the latest Steam version for Windows, it is possible to install games to arbitrary locations by clicking "Install" in your library or the store and choose "Create new Steam library" in the "Choose drive to install to" dropdown menu. There are now also a couple of tools that help with this process: http://stefanjones.ca/steam/  and http://www.traynier.com/software/steammover There is now native support for this feature  on Windows. One way is to simply install two separate copies of Steam, one on each drive. If you know the location where the game will be installed before installing it, I don't see anything stopping you from making a symlink to a particular game and then installing.  You can set up multiple steam library folders in settings (even on separate drives), then go to the game(s)