% mkisofs -J -r -o myimage.iso data_dirmyimage.iso is the name of the image file created, data_dir is the directory containing the stuff you want on the disc. After this command completes (how long it takes depends on how much stuff is in data_dir), use Disk Copy to burn the image to DVD.
[robg adds: I'm not sure if there's an easier way to do this, but I don't want to risk a DVD-R on testing theories; if you either test this or know of an alternative solution, please post your results...]

