Do you mean "SP.DLL"? I had this one on Win98SE. AVG7 detected it but couldn't fix it. I downloaded Spyware Doctor from www.download.com . This seems to have done the trick.
use "CWShredder"...it'll take it out. You can get a free trial version.
Your PC is missing a small driver. Go to any search engine, type in the .dll name, find a site that offers the driver and download it. Drop it into your Windows System folder and the pop up will go away. Make sure you spell the driver name correctly in your search engine!