MS Explorer hijacked

I have an XP system, completely updated to SP2, with AV and now running zonealarm. The browser seems to be hijacked, and keeps going to a seach page, but not all the time, say one time out of 5 or 10 times. Also there is a tool bar and many pops up that I can not get rid off, that are really slowing down the system

I enabled POP up blocker in XP

However, the following sites are listed as expections

Lop.com
mysearch.com
www.iop.com
www.mysearch.com

of course I remove them, but they keep re-appearing. I also removed the tool bar from Add/remove programs, and this also keeps re-appearing.

I have run the most recent SPYBOT and it removed many threats, but still these keep showing up. I would like to recover the system, without having to do a complete re-install. Any suggestions?