Go to Utilities - Boot Camp Assistant . Right click to "Show Package Content"
Then in the folders - Content - Resources , there is DiskImage.dmg . Mount this and you will have a file called "Install Macintosh Drivers for Windows.exe" . Copy that to your Parallels shared drive and run it . You'll end up with it uncompressing all the drivers to C:\Program Files\Macintosh Drivers for Windows XP 1.1.2 . In here you will have C:\Program Files\Macintosh Drivers for Windows XP 1.1.2\iSight and you can do the manual driver location in the windows device install.
I'm going to throw up a how to guide somewhere on the web as i got sick and tired searching the web and coming up against a brick wall or being told the only solution was Mercury Messenger ..
thats kind of how i ended up doing it, but i now have stand alone drivers from the install that i'll be making available so people don't have to go through what i did again 🙂