What OS are you running? I'll assume it's XP sp2. But advice will work for sp1 and win2k also.
OK, Try a run with the MS antispyware program.
MS Downloads
You will have to have a legit install of your OS.
Then Turn off the messanger service.
Then replace your host file with the one attached.
I don't see a good AV program in your list. What are you running? Is it still updating?
Are your MS patches up to date?
I would also recomend that you switch to Firefox as a browser. Ver. 1.5 was just released. At the very least turn off the popups in IE.
Use safemode and MSConfig to controll what loads untill you get it fixed.