There is a hotfix available from Microsoft for the symptoms you are
describing.

FIX: When you run Windows Update to scan for updates that use Windows
Installer, including Office updates, CPU utilization may reach 100 percent
for prolonged periods
http://support.microsoft.com/?kbid=916089

--
William Crawford
MS-MVP Windows Shell/User

"Piet Slaghekke" <p.slaghekke******.com> wrote in message
news:1162974634.563348.11690@b28g2000cwb.googlegro ups.com...
> Problem: SVCHOST.EXE uses 60-100% cpu at bootup or when Microsoft
> Update is running.
>
> CAUSE: Bug in Microsoft Update (Microsoft Update scans all Microsoft
> software including office/
> Windows update only scans Windows for updates)
>
> FIX:
> go to windows update and check if the "get microsoft update today"
> banner is there, if it is then this is not your problem, if it's not,
> click on 'change settings' on the left, in the next window scroll down
> and un-tick microsoft update and click on 'apply changes now' , you'll
> now be back to windows update only.
>