So I have a bunch of imagaes moving accross the screen and I want them to slightly distort (fisheye effect) as they get to the centre and then as they move off the other side of the screen go back to normal. Any ideas on how to pull off this effect?

What software are you using?

With After Effects, you could make a pre-comp of the animated pictures, then bring that into a new comp that has a Displacement effect on an adjustment layer. The B&W image used for the displacement would be a blured white circle in the area you want the "fish-eye" effect to be.

Thanks for the tip Nick, yeah I'm using After Effects, I guess that would have been some helpful info. :-)