I recently removed a nasty Alureon-K virus. I seem to still have some residue or residual damage. I cannot get my XP Pro O/S to update because i am somehow not the administrator any more. I have 2 user accounts, both of which are/were administrator. I tried setting up a new admin account, but to no avail. There are several other issues relating back to the loss of admistrator control.
Viruses tend to kill Windows update, and they also change user rights, services, etc... Removing the virus does not fix any of that. Did you check to see if your account is actually an administrator or not? If not, you'll have to find an account that IS an administrator and use that to make yours an admin. The account actually called "Administrator" should be on the system.
I'd just back up your files and settings and re-install Windows. Trying to hack a fix together after a virus attack can be more of a waste of time than just doing a clean installation.