Windows Update

Hi,
Theres a setting in group policy that will do this. If you are using domain gpo's then activate it there. If not then on the local machine run up gpedit.msc and browse to the user config\admin templates\windows components area - I believe it's around there somewhere....

Assuming that you are using AD and group policies:

Open Group Policy that will affect user(s) that you want to block from using windows update. Drill down to the appropriate policy.

User Configuration/Administrative Templates/Start Menu & Taskbar
There is a policy called "Disable and remove links to Windows Update". The explain tab gives a detailed explaination of the policy.
Enable the policy if it is what you are looking for. Of course, as with any policy I would test it before I rolled it out to production.
Good luck.