hy i have the same problems wiht limewire, it always runs on its own and when i have deleted it an error massage appeared.
same syptoms: strg+alt+del doesnt work, can't open regedit and so on

i have searched my prefetch folder but there is no winupdate.exe file or something like that.
i also have searched the registry like you have suggested but also no succcess!
when i open the the taskmanager an insatller is running, and i t shows 54 processes. when i close the installer limewire stops to pop up and two processes dissapear (msconfig.exe , wmiprvse).

so far so good but i can't fix the problem i cant find the bug to delete it!

there is a file named WMIPRVSE.EXE-28F301A9.pf in the prefetch but i dont dare to delete it!

i have tried with ad-aware, spybot s&d, windows defender, norton but nothing does work they cannot find a bug!

Since a few days norton shows a message after bootin my computer thaht it has found a bug called backdoor.trojan and that it has delete it but problem with limewire is still there and when i reboot my computer norton shows the backdoor.trojan-message again!

i really need your help!

ps. sorry for my bad english!