If you are reading this article you have probably encountered the same problem I have with svchost continually using 45-50% cpu usuage. Making use of Systinternals process explorer I discovered it was the DNS Client that was using up all my CPU time.

Having a look at several forums online most of the solutions were for Windows XP which didn't work for me and were based around the Windows Update service causing the issue. However my issue started after me implementing a whole raft Windows updates recently.

Anyway long story short my temporary fix has been to disable the DNS Client in Windows Services for now. You can get to this by typing services.msc from the Start menu in Vista finding the DNS Client go to properties and under Startup set this to disabled. You may need to go into Task Manager selected services and End the process tree for the svchost service for this change to take affect without rebooting. Disabling the DNS Client basically causes Windows Vista not to cache the DNS entries effectively making browsing sites you have already seen a lot faster. This is by no means a permanent fix, but until now it will do until Microsoft can issue a fix for the issue....I miss Windows XP...