Hi, i did scannow last night but am doing it again right now.
I see that i also got redirected to 'ebay' whilst clicking on one of your Google links/searches you privided me with. I have also got redirected when i have used Firefox/IE today too.
Maybe an infection is to blame for both problems?
Come to think of it, last night i downloaded a perfectly legit (i thought?) programme called BDlot DVD ISO Master to copy a DVD i have. I used the 'convert to ISO' option and it created a winzip folder which i unzipped and it kept unzipping and wouldn't complete and filled up my hard drive, this is when i tried to delete the file and came across the problem with Windows Explorer!
The software was reviewed here: Pcadvisor so I am assuming its not that. You say you have scanned for nasties and found nothing. This is a puzzle. I wonder if the Event logs will give you any clues. But I must admit it certainly would seem you are infected.