Browser hijacked removal failed

[Charles12345]

Hi, I was cleaning a client`s machine that has a new license of SAS pro. His special case is: he only runs xp with SP1 because of an expensive design software update that he would need to purchase before going to sp2 or 3. He`s running zone alarm and avira premium av. SAS removed a great many trojans and hijackers but not all of them. I have disactivaed system restore but whenever i conduct a search using firefox v3.5.2 it will lead me to other pages. e.g. a search for antivirus leads me to spywarezilla, etc. Updates on SAS will not function, however it was just installed, and also his av will not update as well. I have tried as well combofix and smitfraud, same result. I saw that his DNS was messed with so I put back to auto. Also his hosts file has been replaced with a known clean file. BTW SAS scans on this machine are taking over 3 hours. Any advice?