Share your iMovie Project as a File. You can then use that file to create your dvd. Assuming that you don't have iDVD, you can use Toast as TheMacApple suggests, which is expensive.
You could try Burn, which is free and does pretty much what Toast does; ie, creates a dvd that you can play on DVD Players. Just ensure that you create a Video DVD. http://burn-osx.sourceforge.net/Pages/English/home.html