I would ask Google, but I believe you can, provided that they are not excessive. Now, what is excessive when it comes to pop-ups? To me, one, to others, who knows? The specific language that leads me to believe this is allowed is: This is under the Site and Ad Behavior section of the Policies. You cannot place the adsense ads IN pop-ups, though.
See my post above, I think you're alright depending upon how many pop-ups there were and providing that adsense was not on the pop-ups themselves.
Well, why do you want to use pop ups. Everybody hates pop ups. If I visit a site and there a pop up appears, I never visit it again.
No it is not against TOS. Please quote the portion of TOS/Policies which says no adsense on sites that have pop-ups.