The 100% CPU usage on start by svchost.exe is caused by Automatic Update (oddly enough this seems to be the case if you got Office 2003 and not with Office 2007..i suffer the same since i went back from 2007 to 2003 version). I advice you to turn of automatic updates for now (Microsoft will probably come with a working fix later this month) and frequently check for updates manually.
Also see:
svchost.exe 100% CPU on startup
ComputerWorld - Microsoft's fix for Automatic Updates lockup not working
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