My suggestion would be to manually re-install each ThinkVantage app that is corrupted (including System Update). If that doesn't work, than you'll probably will need to restore the hard drive to its factory-installed state (especially if there are other non-TV apps that are corrupted). I had a similar experience to yours recently and I had to just that (I'm using XP as well).
OR, can I re-install System Update, uninstall the others and let System Update find and install the apps?
You can try that as well.
OR, is there a better alternative to TV's Access Connections?
You can always use the Windows one. I personally prefer Access Connections, as I think its the better one (but that's just me).