Reinstalling iTunes

Uninstall software, remove programs and solve uninstall problems
http://www.revouninstaller.com/

Removing and Reinstalling iTunes, QuickTime, and other software components for Windows XP
http://support.apple.com/kb/ht1925

Bonjour issues, see if this helps: http://www.raymond.cc/blog/archives/2008/02/10/how-to-uninstall-or-remove-bonjour-mdnsresponderexe/

Trouble installing iTunes or QuickTime for Windows
http://support.apple.com/kb/HT1926

Windows reports that iTunesSetup.exe is not a valid Win32 program
http://support.apple.com/kb/TS1406

First verify if you have a 32 or 64Bit version of Windows:
1) Click the Start button, right click Computer, and then click on Properties.
2) Under System, view the system type - it will say either 32 or 64 bit.
3) Download the appropriate version using the links listed.

Itunes Download (32 Bit):
http://www.apple.com/itunes/download/

64-Bit download:
http://support.apple.com/kb/DL1037

Verify that the 'Windows Installer service' is running, or force start it to start.

1) Open Run, and type in services.msc then press Enter. Alternatively, go
to Control Panel/Administrator Tools/Services.

2) Locate Windows Installer in the list of installed services.

3) Verify that the Status is 'Started'.
If the Status column is blank, then right click on Windows Installer and select Start.

4) If you get error trying to force start the Windows Installer service,
then change the Startup Type to Automatic (the default is 'Manual'),
and then restart the computer.

5) Very the Installer Service is running after you reboot.

Also:
Apple's Itunes forum: You may find a solution (if none of the above is of any help) to your problem when you post it on their forum.

http://discussions.apple.com/category.jspa?categoryID=150

J W Stuart: http://www.pagestart.com