There is a problem with the way that Parallels 4 does documents folder synchronization. What it does is to point to your home folder on the OS X side with an UNC path. It works great as long as the windows programs that look for that folder understand UNC.
Visual Studio 2005 is not one of these. The first thing that caught me cost me two long miserable hours of troubleshooting. I was installing Subsonic and it would not see the add-in. After all of this misery I realized that the problem was not that Subsonic was broken, instead it was because VS couldn’t see the folder where Subsonic installed the add-in.
Turned off home folder and desktop sync, now everything works.
Like I said, the problem here is Windows (XP), not Parallels.