I recall there being a thread devoted to a rather simple opt-out option for pop unders. It's something that I ran on a previous computer, but that computer is now spare parts, and I'd love to run it on this one.
However, I can't seem to find said thread. I've done a Google search on The-W. I've perused the Internet & Computer forum here. I've even dug through CRZ's World, because I think he mentioned it after it had been around awhile.
Well it's Vista, but much faster and cleaned up a bunch. Some nice new features in there. The reviews are MUCH more positive than when Vista was coming out, that's for sure. As for upgrading, the system requirements are pretty much the same.