Sorry about late response; I hadn't put the thread on email notification.
640x480 is doable, but I found I needed the tetsu or cacko kernel with overclocking. Even though I successfully flashed the kernel, I don't use the overclocking after all. It's battery-intensive, and w/ default cpu speed, 320x240 shown in "full-screen," the movie is filling about 3/4 of the screen, and it's crisp and synched. Some movies, even when converted to 640x480, don't fill entire screen, maybe 4/5s or even 3/4s.
So on a trip, without a/c, I'd rather go stock speed and give up a quarter of the screen and watch more movies.
The great thing about DVDCatalyst is that it converts to practically all known phones/pdas/computers. My lucky wife just got an ipad, and sure enough, there was a DVDCat conversion setting for Ipad, no handles to jiggle, and she was off and running.
Jake