You can get 775 boards that support agp, but they are crap. You can get boardsd that supprt BOTH AGP and PCI-E, and they are even crappier! It's like getting a board that supports 478 and 775, made by ASRock. What a crappy board.
I meant 'CAN' not 'CANT', my bad. I was slightly in the bag when i typed that.
You can get a 775 board with an AGP slot, but they are crap. Even made by very reputable companies, they are still the lower-end boards that those companies put out.