I did the exact same thing you want to do, no joke. Here's my set up:
160 gig = Windows xp
40 gig = Linux Unbuntu
I just installed windows xp like normal on the 160 gig drive and then installed linux to the 40 gig and it did a dual boot automatically. Except my linux OS is the primary operating system. Any one know how to make windows the primary one?
Bigk