(I’m assuming this is a DV project,yes?) There is more than one way to do this, but with iDVD4 AND wih a video that’s over 20 minutes long, this is what I consider the easiest way:
Run your entire video out to DV tape over firewire. Then, shut down Final Cut and open iMovie. Use iMovie to re-capture the video. Use Apple-T to trim off the black at the start and end of your timeline. Then, create your chapter makers in the iMovie timeline. (Look in the DVD section of iMovie to see where you do that.)
Once you’ve made all of your chapters, you can click a button in iMovie that transfers your project over to iDVD. Yes, the outputting and re-capturing takes time, but once you’ve gotten to this point iDVD will not only take all of your chapter points but it will also create menus with links to each of those chapters and name them what you’ve called the markers. It will do most of the work for you. All you have to do is go back and change the syle of the menus to look like what you want them to be.
If your video is LESS than 20 minutes long you can export it from Final Cut as a Quick Time movie and then just import it into iMovie. Anything over 20 minutes would have to be broken up into small files, however, which is why I say to use tape for longer projects. It’s just easier than splitting your video up and fixing it later.
(Before you do any of this, make sure that your iDVD prefrences are set for the proper video length, in other words, less than or more than 60 minutes of video.)