I am having the same problem. Norton and Spybot don't get it. I will chqck bak later to see if someone who had had this problem says what got rid of it.
It sounds very much like a Browser Helper Object (BHO) that has been added into your system by a nasty.
Download a copy of "HiJackThis!" and it can show what items you have on your system. Most are good and should be left alone. But some can create problems like this redirect behavior.