I have a dual boot setup with XP Home (on primary) and Vista RC1. Whatever problem people had with installing Vista on a logical partition does not seem to be a problem with RC1.
Interesting Note:
While in XP, the primary partition where XP is installed on is assigned a drive letter c. The partition which RC1 is installed can be viewed in XP under driver letter d. Normal expected behavior.
While in RC1, though, the primary partition that XP is installed on is assigned a drive letter d, while the 2nd partition that RC1 is installed on is given a drive letter c.
Some games I installed in XP will run fine in RC1 without reinstallation, but may crap out when trying to load/save game possibly due to the reasons given above.
I'm running the 64-bit version, btw. To those complaining about 3 or 4 gig, the recommended free HD space for Vista is 15 gig. I haven't even began to install anything major and it's already taken up 13 gig.