For my own personal preference. I would split the 120 gig into 2 parts, an 80gig and a 40gig. The 80 gig for storing files (word processing documents, weird downloaded stuff, music, videos) and the 40gig for eseential computer program installation files (mouse driver, video card driver, printer driver, keyboard driver, ghost image etc.) or to serve as your main drive (where you install ur OS). the 40 gig drive can be used for eseential computer program installation files (mouse driver, video card driver, printer driver, keyboard driver, ghost image etc.) or to serve as your main drive (where you install ur OS).
Setup 1:
Drive 1: 40 gigs for main drive
Drive 2: 80 gigs for misc files and 40 gigs for essential computer program installation files
Setup 2:
Drive 1: 40 gigs for essential computer program installation files
Drive 2: 80 gigs for misc files and 40 gigs for main drive
Since the other guy said that drive 2 is faster because of it's 8mb cache and higher density platters, i would use setup 2.