imovies and Burn software/burning to a DVD

I know this question has been posed before, but I am still having trouble. I have several long home movies (ranging from 2 hours to about 3.5 hours) that I created using iMovie. I want to burn them onto a DVD that myself, and parents/grandparents, etc. can watch on a regular home DVD player. I don't have iDVD, but I downloaded Burn, as others suggested. However, when I launch Burn and try and follow the tips others have posted, I get the stage where I am supposed to select my file, and the iMovie Theatre (where my movies are stored) is greyed out and can't be selected. Any help would be really appreciated. Thanks!