Do they say what frame size they want? If it's suitable for iPod or iPhone or other mobile device, you can use H.264 with a bit rate around 1.5 Mbps (like Apple does). If you need full HD at 1920x1080 then you'll need Blu-ray type bit rates of about 20 - 25 Mbps (or higher).
Obviously, 2 hours of feature film at 1.5 Mbps will be a much easier file to move around than one created at 25 Mbps.
NB: Bit rate and duration are the only factors that affect file size. Frame size doesn't affect it at all. The only thing frame size affects is whether a particular bit rate will look good or not.
Jeff
