[header] How to install os x lion on an external drive [title] Download mac os x lion from the mac app store. [title] Connect the external hard drive you want to install os x lion on to your mac. [title] Navigate to applications] utilities] and double-click disk utility. 
[title] Select the hard drive you connected from the pane on the left within disk utility. [step] Note: be careful, this process will erase everything on your external drive before installing lion.