I know this is somewhat of an old post, and im not sure if anyone has found a fix for this. However, i found one that might work. I used to map the network drive in the "my computer" area, thats where i would link my documents folder when changing its location. However this always yielded and error 1327 invalid drive with installshield.

I changed the physical location of my documents to my server, but i right clicking on "documents" folder going to properties, location , clicking move and using the network navigator to select the machine and folder and NOT a mapped drive. \\"networkshare"\"destinationfolder" After doing this i attempted to isntall a program i was having an issue with, and it installed fine.

i use widnows 7, X64 ultimate, but im sure this will work with Windows Vista. if you have any questions just ask.