What's the right way to upgrade Parallels Tools?

I had the same problem - MBP 2.16Ghz 2 gig RAM
I have my OSX documets folder shared through parallels, mapped as a network drive and set to the Windows "My Documents" folder - it's mapped to drive D:
The Tools install image did mount in the CD-ROM drive but would not install because it was on a different drive letter. It would seem that an installer should be able to execute without caring where it is. I didn't have this problem with other upgrades. At least my number pad enter key is working.
1 step back & 1 1/2 steps forward.