You don't need a javascript forum, it sounds like you need a security forum. Has your home page been hijacked also? What site is the persistent popup taking you to? Such things provide clues.
Whatever the case, running AdAware is usually the first defense:
http://www.lavasoftusa.com/
After you install it, check the reference file on the front page and make sure it matches the reference file being used (which will be on the bottom of the AdAware window). Sometimes the new reference file does not make it into the installation packages and you hafta update by hand.
BTW: It probably got populated via ActiveX. Disable that shit.