How big is the file? If you export your finished product from iMovie, you should be able to choose a variety of compression levels. To be able to play it in a DVD player is another matter entirely. I'm assuming you mean a standalone, home-theater type DVD player, and not attached to a computer. I'm not sure if DVD players can decode Quicktime, I'm going to guess not.
I suppose you could send your iMovie file to iDVD, then export to a disc image on your hard drive. Then use something like Handbrake to encode the TS_Video file to something smaller that would fit onto a CD-R, but preserve the DVD compatibility.
As far as I know, this isn't an easy task. Maybe someone else who does this regularly will stop by this thread.
Cheers.