I'm pretty sure there is a way to make AdSense open in a new window. It's not a popup, it a whole new window, just like you clicked on a link that was coded for 'target=_blank'.

I was thinking about doing this myself at one time and I did find a javascript that did it. But I never went ahead with it since it does violate AdSense TOS. If they catch you doing it, you're history.

However, if anyone's interested in the code, PM me and I'll see if I can find it. But just keep in mind, you could lose your AdSense account.