Meaya POP UP BLOCKER WORKS GREAT.
Something a lot of people are confusing are pop-ups and adds.
Pop-ups are just that.... but some sites have payed for advertisments that no add blocker will stop.
ALSO to stop msn messenger pop ups go into c:\ programs\messenger then find the .dll file named msgsc.dll.
Now change the name of the file (right click) then call it msgsc.bak.
Make a backup copy of the file and store it somewhere (before you rename it) incase of an error.
PS. always ..always ...always! do a backup before changing any settings in XP.