Alright Raver, I'm giving you my clean install instructions. Please read them over before you step through them to be sure you understand them. Remember to follow the steps VERY carefully, otherwise you could cause harm to your PC.
1. Uninstall itunes/ipod/QT software. Delete any old installations you might have.
2. Reboot your PC
3. Re-download the itunes installer and QT and save this installer to your desktop
4. Go to C:\WINDOWS\Downloaded Installations. You should see folders like {06EB3288-C5F4-4C73-8EEE-AC798668FF66}
5. Look in each of these folders for itunes.msi and delete the folder. Be careful to only delete the folders
containing itunes.msi
6. Clean out your temp folders, Delete as much as you can in these folders except for the folders Cookies, History, Temporary Internet Files.
a. C:\windows\temp (if one exists)
b. C:\Documents and Settings\{username}\Local Settings\Temp
Sometimes installers will pick up old files or won’t delete their temporary files.
7. Go to
http://www.download.com/3000-2094-881470.html and download the regcleaner. Unpack it and run it. This is a nice utility that will delete broken registry entries and create a file with them. This way if it deletes anything needed you can add it back. Note I never had to do this with using it for many years. Also it doesn't list XP but you'll be fine. I run XP on both.
8. Empty your recycle bin. Reboot your PC.
9. Now try to go and install everything again. I'd do QT first then follow with itunes. Remember to disable virus/firewall/privacy/web accelerators before launching the install.
If you still can't install then I might need a install log. However I'll give you those steps if these don't work.