I can find plenty of people with this problem, but no solutions.
Do you have any problems with installing anything else?
Presumably you have a working old version of iTunes so I don't want to suggest anything destructive.
If you want to try the install log thing, here is how, but I fear you don't even get that far.
Open a cmd Window – Start>>RUN CMD
Drag iTunesSetup.exe to command window to get full path
Then after it type a space then:
/l*v C:\log.txt
The installer will create a log file c:\log.txt
If a log file is created, there might be an error message at the end of it.
I wonder if it is worth seeing if the Quicktime installer works, you can download a version that doesn't include itunes here:
http://www.apple.com/quicktime/download/win.html
That might help show if this is specifically a problem with the iTunes installer or if it affects something else.
P.s. I meant to say earlier did you try turning off virus checking when running the installer?
Message was edited by: polydorus