I use this little bit of software every day, and 
I have been for about 3 months now, with NO 
problems. It works flawlessly. When a new window 
spawns, it automatically kills it. It runs in 
your taskbar and you can turn it on and off as 
you please. It's called "Pop-Up Stopper."

If it's active, you can hold down the Shift key 
to let a new window spawn if you need it, as some 
websites launch links in new windows, and 
sometimes you just want to have 2 or 3 IE windows 
open.

I'm not sure how it works with Netscape, though. 
I always use IE.

So just go get it and your pop-up problems will 
be solved! (ugh, I sound like a salesman)

http://www.panicware.com/product_dpps.html