Sorry for resurrecting this thread but I might have some help, or not. I had the same problem, updates would download and verify but not install and decided to try and find the missing pieces the hard way. Trial and error that is. 18 installs later, using Windows XP Home sp2 (eng), I can confirm that the missing component is Operating System Options/Logon Notifications. That one must be kept. However, I also found out that I don't actually need either COM+ or DTC. SENS alone will do. Sure the SENS service can't run without those two but Windows Update doesn't need the service, only the files it uses. This might be particular to Home only though, using the x64 Pro trial Automatic Updates and BITS depended on the COM+ service. Hopefully this will help someone else as well. Now, to try and find what I need to keep to get my Creative Gameport working.