You may need to get hold of another media (worst case screnario)
run the setup.exe as an administrator, by right-clicking the setup.exe file and choosing run as administrator. (even though you user account may have admin rights, still follow this instruction)
Reason for this that to better protect Vista, Microsoft decided that its built-in Administrator account should be disabled by default. So the built-in Administrator account is now disabled in all clean installations and upgrades of Windows Vista.
Hope this helps.