I recently tried to install Adobe Acrobat Reader v8 on my pc running Vista Ultimate 32 bit.
It started installing then came up with the message that either the hard drive it was installing to was full or that I didnt have permission to access the Temp folder.
There was plenty of room on the hard drive and I had all permissions set for admin rights for myself
I ended up installing v6 instead, which installed ok.
Yesterday I needed a newer version to read a PDF file so decided to find out why v8 had a problem.
It appears that because I had turned off the UAC (User Account Control) then I couldnt authorise Vista to continue at the point where it needed to access the TEMP folder so it assumed that I didnt have permission and stopped the installation
I enabled the UAC and rebooted and then the installation worked without any problems, as I could click on Continue when it asked for permission.
I then disabled the UAC again and rebooted.
This may affect more programs when trying to install them but thats the first one I have come across that wouldnt install because of UAC being turned off, so far.