#1 The first thing you need is a decent computer:
1 - 500 meg or more Ram - (1 gig recommended)
2 - Decent processor - P4 or equivalent
3 - Enough harddrive space to hold large files - 100 gigs recommended but not necessary.
#2 Get a decent sound card to transfer music in and out of your PC - eg Maudio Audiophile 2496 ($135) - pretty good card.
#3 Get recording software - numerous packages out there including many lowbudget ones that will work fine - Cubase, Guitarstudio etc.
#4 It's helpful to have a midi keyboard to program keyboard, bass,
drum tracks but not absolutely necessary.
Hope that helps.
G