Lecblue's site and Paul H's site have some useful info on media choices, if you haven't seen them. Personally, I've had better results with AVIs then with GIFs. This is partly due to a known problem that Internet Explorer has with playing back GIFs (they slow down). I've had better results with Smacker than with AVIs, but you need a special player to view Smacker videos. The same company that makes Smacker has a newer product called Bink. I haven't tried Bink, but unlike Smacker, it's not limited to 256 colors.