Bluto...again with an incorrect answer...dumdass.
No, not all AGP slots accept all AGP video cards. In the early days there was a 1x AGP slot. Most newer video cards will not work in 1x mode, i.e. 9800Pro is one.
Also there are a very few cards that actually use an AGP 2.0 port that had a slightly different footprint. Remember back when there was a tab you had to flip over to use with AGP 2.0 cards only?
So the answer is...no. Not all AGP cards will work in any AGP port.