Thanks. We also have a pretty sensitive fire-wall installed in our wireless router; it keeps out a lot of stuff. I'll have to be sure to instruct the kids never to click on a banner ad!
Good luck with the kids. My teenage son's friends love to use our computers and I think their web-surfing is the source of most of the spyware. Of course they deny everything. I'm pretty indulgent about this sort of thing because I'd rather my son and his friends were at our house than someone else's but I think that sometime next year we'll get one of those slick flat-panel Imacs and end the problem for good.