I am playing the game, quite smoothly, with:
AMD 64 3500+ (single core)
2 gigs PC3200 Kingston Ram
EVGA Nvidia 6600GT (PCI-X16)
Seagate 250 3.0/gbs (SATA II)
Creative Labs Soundblaster Live! w/ 5.1 speakers
Not a blazing rig, but it can handle SH3 with no problem.
Oh, and do not, for the love of God, buy a computer. Order the parts and build it yourself.
www.newegg.com is all that you need, and
www.dl.tv has a full breakdown on how to buy, setup, and build your computer from the ground up.