to answer your last question, yes, if you can do offer the option.
Otherwise it's a balancing act between having the right compression for the right size and the right length of film.
If you need a large viewing area with crystal clear imagery of a video that is 10 minutes long, its unrealistic to think people running 56k or even dsl would have no problem downloaidng it
Other than that it comes down to how much are you willing to sacrafice in the video for download options. Get yourself setup if you can on a streaming server or play via flash which has streaming capabilities, and limit your data rate to x/kbps
