There've been a collection of issues around the Windows installer, but this
message isn't typical of those, as far as I can see.....
What about deleting everything in the temp file directory and any
subdirectories of that?
I do that at a cmd prmpt --landing at \documents and settings\username, and
doing CD local settings, CD temp.
At that point you can run explorer . and clear out nearly everything--there
are usually a few .tmp files that are in use, but most stuff can be deleted.
I've seen some wierd errors when a setup program couldn't write to a
subdirectory, or that subdirectory didn't exist for various reasons.