ok I am new to 7 and haven't played with Ultimate (i have home premium version). I know that Ultimate has more features for connectivity and such. looking around, I had found one discussion on bleeping computer about this in XP so you might want to check this out and see if it helps. BleepingComputer.com > Svchost.exe Network Service 99%
The first thing addressed is about possibly having a virus, but I can't say this is the case. Do a scan anyway if you have not.
The second point is that svchost.exe as a process has services running in it. if you can post a list of all of the services that svchost.exe is running. you can find this by right clicking on process and going to properties. look in In the services tab and post back with a list or screenshot of all of the services running under svchost....Hope this helps