I realise this is an old thread, but after Googling my problem this was the most useful thread I found, in my opinion *is* still useful, and it helped my solve my problem (it appears).
I had similar problems as described just recently with Windows 7 of CPU at 100%. For example, my Windows Media Player Network Sharing Service was hogging a lot of CPU, also saw Task Manager at way high CPU whilst it was open, had Firefox and some other applications maxing out the CPU for no apparent reason, I've also seen the HD Audio process hogging CPU. I stopped many Services and disabled a number of items from startup.
In the end, the problem seems to be because I had recently changed to the 'High Performance' power plan, which in Control Panel > Power Options > Select a Power Plan > Change plan settings > Change advanced power settings > Processor Power Management > Minimum Processor State > Plugging in (which is what I have most of the time), the setting was set to 100%. So it seems that this setting is causing my CPU to *overwork* somehow (seems silly to me).
Changing the Power Plan to 'Balanced' seems to have fixed the CPU maxing out problem...! Yay!
So I wanted to share it on this thread as it seems to have helped a lot.