Hi gopal,
Did Dr. Web put c:\windows\svchost. exe in quarantine?
If it did then do as Tech said about turning off System Restore - this will delete all your restore points which is the only way to get rid of the infection hiding there. You can turn system restore on again later.
Also delete the temporary internet files. I like CleanUp for this since it will mark files for deletion on reboot if necessary
http://www.stevengould.org/software/cleanup/If you use CleanUp make sure the Delete Prefetch Files option is not checked (deleting these can temporarily slow your computer).
Scheduling an avast! boot scan is fine if you want to do this but, since avast! hasn't been identifying the problem, I would either substitute another Dr Web scan for Tech's step #3 or add Dr Web as step #5. In either case you need to reboot first.
You can enable system restore at any point after the Dr Web scan if you wish as long as you are coming up clean.