Has anyone got any advice on the size and format for videos that will be linked not embedded and shown fullscreen.

I am creating a presentation that will be shown through a projector with some of the slides showing full screen videos and am worried about the output quality.

I created a test video in After Effects with PAL DV (720 x 576) but when inserting into Powerpoint it is not big enough to fill the slide. Is it ok to stretch the video or should I have created the video at a bigger size in After Effects?

Also what is the best video format for this type of work (wmv,avi etc)?

Any advice much appreciated.