while coding, iDVD needs est. 12 Gb of "hidden" file space on your start volume; hidden because you cannot see it in the finder and it is erased after coding.
i'm doing my private videos on my good old Cube, 450MHz, 832 Gb Ram and a "external internal" ide connected superdive (i prolonged the internal IDE to the outside of the Cube to be able to use iDVD). for a 40min video this combo needs 12 to 15 h for coding, iLife3 of course, 04 is not supported