You've picked up GATOR, GAIN, or CYDOOR .... basically spyware that triggers popup adds by certain keywords on websites ...
To remove it, download and run AD-AWARE (
http://www.lavasoftusa.com ) ... it is freeware, and will locate ALL spywares on your machine and give you the option to remove any or ALL of them ...
Run AD-ADWARE once a week ... make it your friend !!
NOTE: If you are running Kazaa, disabling/removing CYDOOR wil cause Kazaa not to function ... Kazaa is driven by its ads/popups
There is a work-around though ... install Kazaa LITE (
www.kazaalite.com ) KL has no ads or popups ... be very careful though ... KL will tell you the DLL file not to disable from ad-aware ... write this down and be sure not to remove it ... or your popups will return ...