Optimal Image Formats?

I was working on my portfolio site and when creating a photo gallery that consists of an image scroller, I noticed that trying to move even 4 jpg’s loaded dynamically is extremely sluggish. I would like to have nice smooth movement. (its running at about 30-40%+ of cpu on a 1.4ghz and I want more img animations) Do png’s work much better than jpg for speed, or is there another file format that would be best? Any suggestions???

Thanks in advance!
-freeskier89