I found a strange error when users were installing trials of Adobe Photoshop (or Acrobat) in Vista. They were getting "Error 1327 : Invalid drive H:"
As per the information here:
1. Right click on Command Prompt in the Start Menu and selected Run As Administrator.
2. Typed "Net Use h: \\servername\sharename"
3. Exit out of the command prompt
It's something ridiculous about the user's home folder on the server not having full administrative permissions which I guess it needs as a temporary folder.