im in the same position.
ive started on garage band, tryed logic but a bit too advanced for me.
get ilife09 and the new version of garage band, and just try the drum loops, some are "editable".
For input i can highly reccamend the Line6 UX1, althought you might want to upgrade to somthing like the
http://line6.com/podstudiokb37/ to have a midi input? with the gearbox program i used to (pre-snow leopard UPDATE PLEASE!!!) be able to use various guitar/bass amp+FX modeling, also does Vocal MIC/FX modeling too.
i mainly just line-in guitar/mic with the UX1 and take it from there. with cover songs i import midi tracks of songs to GBand, delete everything but the drum track and record bass, synth/piano guitar an vocals on top.
if your just starting out recording that should help you, only go for a more professional system when you find garage band limiting for your needs... ive established all i need is to record, adjust the levels and use minium FX, odd bit of 'verb and EQ tweaks here and there.