My laptop has dualboot into Win2k for work and WinXP for home. I have my smartphone setup to synch with two computers. I first setup my number one, main synch profile with my Home XP boot which synchs with everything. I then have my second synch profile with my Win2K boot. On that one I only allow it to synch the calendar as I don't want all of my company's MS Exchange contacts on my phone
It's really simple. After you setup your first synch profile when you connect the phone to the 2nd PC, just develop a profile with it but chose the option that you'll be synching with two PCs. Then chose what it is you want synched.