Are you using Maya 6.0? If so, just checking the 'use image sequence' should load all of the images so you can play them through. If not, simply type in =frame; in the box next to where it says 'frame extension'. Pure_morning's right about frame padding too, try to make sure your using 4 padded 8 bit tiffs.

If your going to be doing some matchmoving, are you using Maya Live? There's a massive thread somewhere on this forum where I've been helping out some people with this. Just do a search for it if your interested. You will need to track the camera if you want to integrate a 3D element with your moving backplate.

LisaG