Smoothing out jagged edges during slideshow of digital stills

I'm doing a slideshow video using over 100 digital still pics in a Vegas 6 NTSC Widescreen (720x480i) video.

The jist of the whole project is to show each digital still for 5 seconds as it slowly zooms-in....using different angles.

While viewing the final presentation on DVD the stills seems rather jagged as the video zooms in on each still. Its not interlacing flicker, just jagged-edges dueing the zooming in.

The stills in this video project are in their original size which is 3872x2592. I chose to keep the original size because the slideshow slowly zooms in on each pic & I want to avoid pixelation while zooming in.

So....

what should I do to cutdown on all the jagged-edgyness I'm seeing???

could this jagged-edges be from the huge original size of each still pic? should I reduce the size of the still pics in Photoshop Elements?