When ever im surfing on the internet winfixer 2005 takes over my most visited webpages saying I have to download it I click on the x to close it out and it still promps itself and takes over. I have downloaded microsoft antispyware, ran it found spys cleaned it up. Ran symantec antivirus didn't find anything

(heard this wasn't a real good antivirus) I did a disc defrag, cleaned out all internet files still can not get rid of the winfixer 2005.
What can I do to get rid of this?