7-31-09: Today I found that 12hippos posted the same project as me, but about 6 months earlier. Please note that I did not copy him, as I did not know the instructable existed. If you really want to see heres the link. http://www.instructables.com/id/SUPER_Cheap_Airsoft_Pistol/
Step 1: Get your supplies
You also need caps. I got a pack of 24 cap rings for a buck at Albertsons
You need airsoft bb's (of course). You can get these at wal-mart or any sporting goods store.