Direct X 10. (upgrade) Video card?

What do I need to know before buying a video card with direct x 10? I am trying to squeeze a little longer out of my old agp computer before buying a new one. I want to wait and see what new video technology is coming out in the next year or so before I decide on a new rig. I see some of the agp cards on newegg have direct x 10. Will direct x 10 work on any agp technology computer?