For a while now, whenever I start my computer at work, I get to wait about 5 minutes with my CPU up to 100% due to svchost.exe. Of course, this being an important component of Windows, I cannot delete or disable it, neither can I see what subprocess is causing this utilisation with the normal Task Manager. However, one can download Process Explorer and see a lot more information. I highly recommend it.
Anyway, back to the original problem. I noticed that the problem was the ntdll.dll (ntdll.dll!RtlAllocateHeap+0x18c to be exact) which is, again, a Windows important file.
Only googling to the extreme did I find that the issue is caused by Windows Update, scanning your computer each time you start it. If you disable Windows Update, you don't get the updates, but you get rid of the wait.
Here is a discussion with Microsoft MVPs about possible solutions.
Also, try this link.
And if you do have Process Explorer, you can set the priority of the offending task to Bellow Normal, which will allow you to run any program normally while the Windows Update process runs only on spare CPU. Normal Task Manager does not allow you to change the priority of the process.