I had this problem myself. My Windows XP home PC was affected. I tried again at work and had the same problem. At this point I checked my anti-virus logs and noted that during the installation process the file DifXInstall32.exe had been detected as corrupt. I managed to resolve things as follows:
Completely uninstall iTunes following the instructions at
http://support.apple.com/kb/ht1925, then uninstalled my antivirus software. After rebooting, I cleared up folders according to the details on the above page. I found I was unable to delete the Bonjour folder - something else must have installed Bonjour before I installed iTunes. I removed Bonjour after following the instructions here:
http://arai.wordpress.com/2008/02/11/completly-uninstall-and-remove-bonjour-serv ice-and-files-mdnsresponderexe-and-mdnsnspdll/
After this, I cleared my temporary internet files, and re-downloaded iTunes, and went through the installation process again. This time, my iPad was detected.
I think it most likely that my antivirus was the cause of the problem, as I experienced the same thing at work where we use the same av programme.
Hope this helps other people having the same annoying problem. Particularly annoying if you haven't activated your iPad yet!