HI,
I second CurlyBen's advice. I also use Win98se, and really don't get any pop-ups, to speak of.
Please follow his advice, clearing out any Spyware you might have installed in your computer; possibly causing all the pop-ups.
I also use a great, free program, that integrates with Internet Explorer, stopping these Spyware programs from even being installed in the first place.
You don't have to scan with this free program, but you do have to update the "spyware definitions" about every 2 weeks.
If interested, it's at:
SpywareBlaster Update Available
It's SpyWare Blaster; and it really works great. Best of luck.