What steps can help burning an iMovie '09 project to DVD when the program crashes?
I would start by checking out Software Update to make sure that there are not any current updated for iMovie '09. I would then just try to export the project in a resolution of your choice to the desktop (or wherever you prefer), and just use Disk Utility to burn it from there. This will make sure that you at least have a hard backup of the project, and this may be more effective as you're not trying to run two programs at once (as iMovie is transferring to iDVD). This is key as your system may not have enough RAM to do two high-end processes at once (I don't know your system, so this is only an assumption). This being said, I would try to make sure that you have the fewest amount of programs running during this time period I would then try to take the exported project from the desktop, and throw it into iDVD to burn it with the menus of your liking. I hope this helps, and let me know if you have any more questions.

Note: If you are on a laptop make sure it's plugged in, and that you are running a program like Caffeine to keep it from falling asleep during this process.