Quicktime file too big HELP!!

DND

Guest

I have made a movie in imovie and converted it to idvd and i am unable to burn movie because file is too big! Its a 20+min movie that unfortunatly was short w/ 8mm and converted over. I know huge file size, but it is what it is. Anyways i need to find a way, if there is one to either downsize movie or something to fit it on a dvd disk. Its a 21gig file and obviously wont fit on my 4.7g dvd. any and all advice welcome. thanks