Allthough a good advice, a good alternative would be;

Pentium III 550 or higher 256MB ram
Delta 1010 audiocard
CoolEdit pro (as easy to understand as hardware )
A freeware midi sequencer if you have only
one midi keyboard.

If you don't mind studying a lot;
Logic Audio Platinum or
Cakewalk Pro audio or
Cubase VST

additional I would advise a
midipatchbay if you want to hook up
more midi devices.

Keyboards/Sound Units: Kurzweil 2600S, Roland VR-760, Acces Virus C, Roland G-800, Akai AX60, Minimoog, Machine Drum, Roland R8-M, mediastation x-76