For me, shooting "street" is a matter of nerve, and I don't always have enough. My most successful efforts (successful being a relative term - read as, "I took pictures on the street!") were done with the following parameters:

1. Used a rangefinder -- it was helpful to be able to put the RF viewfinder quickly to my right eye while keeping my left eye open to observe the whole scene around me. The RF is much less intimidating, I believe, than most DSLRs would be. A "big rig" SLR used to mark you as a pro, but now every doofus in town is walking around with a massive DSLR with an el-cheapo 5mm-500mm zoom on the front!

2. Used Tri-X film, allowing F8. This f-stop allowed me to focus the camera at approx 8 feet, then not worry about focusing each time I shot - depth of field kept the scene in focus.

3. Kept walking toward my subjects. I took a long walk mostly shooting as I passed people on the sidewalk. People will seldom make an effort to stop and confront you if they are "on the move" - not worth the effort, I suppose.

4. Shot a lot of pictures in "tourist" areas -- particularly in D.C. near sites with lots of other people carrying cameras. As several have indicated above, this lets you "blend in" as you build up your nerve.

5. Always striving to get closer to the subjects. this is tough at first, because my natural tendency is to avoid getting too close to someone and snapping a picture. I really have to work on this!

6. Smile at people. This always tends to disarm anyone suspicious of a roving photographer. Garry Winogrand seemed to be a master at this - smiling and exchanging light banter with people he was trying to photograph (at least when he was being filmed doing his street photography).

7. Don't bother to ask permission.

Rinse and repeat, often!!