I am currently putting together a route map animation over australia, my orginal image of australia as the base was a 5250 x 4320 jpeg, which i converted to a psd and inserted and resized to the comp (720x480), although now when it is coming to render the video the proportions are far too large, as AE still sees the image as 5320x4320.
I have tried to resize the original jpeg in photoshop and replace the file, but when I replace the picture the proportions are still unchanged in after effects.
Also can anyone suggest suitable rendering settings for burning the animation to DVD. The animation lasts about 20 mins
Sounds like your original (large) image is still being used by your AE comp. I would make doubly sure you've imported the smaller image you created in Photoshop, and make sure that the large image is replaced by it in the timeline. You can select the layer in the timeline containing the image, then Alt/Option drag the smaller file onto it to replace.
As for rendering for DVD, I generally render everything out using Quicktime animation codec for the highest quality "master render" possible, then you can convert that to MPEG-2 for DVD using Compressor, or DVD Studio Pro (Mac) or whatever DVD authoring software you use.
It's only work if you'd rather be doing something else...