Questions to ask when buying a recording interface:
1) How many inputs do you need? What type (1/4", XLR, MIDI, etc)?
2) What platform are you recording on? Mac, PC, Linux?
3) What make/model computer do you have?
4) What are you recording? Guitar, drums, bass, vocals, horns, etc? How many things are you recording at the same time?
5) What sequencer are you using? Pro Tools, Cubase, Sonar, Logic, Reaper?
6) What is your goal for your recordings? Post on myspace? Make a CD? Youtube vids? Just for fun? (ie, how important is sound quality)
7) What other recording equipment do you have, if any? (mics, DI boxes, preamps, whatever)
8) How much are you willing to spend?