Your 500MHz G4 doesn't have a DVD-ROM drive? At work I used a 450 MHz G4 that came with a DVD-ROM drive.

To watch DVDs I would just insert them in the computer's CD/DVD drive and use Apple's built-in DVD Player application.

As for attempting to play DVDs via RCA inputs on the computer, I have no idea.

I bit confussed, but I believe that you are trying to use your mac as a monitor to the free standing DVD player.

If that is true then no program is going to help since the mac is acting as a monitor and you would use your remote control that came with the DVD unit to access the DVD. If you can even view it using RCA or SVideo I have no idea, I would think like you do in theory you could.

Since the DVD is not a mounted disc on your mac, you mac is only receiving info via RCA cables, it can not send instructions to the DVD player to access the DVD information itself.

I believe that your best bet is to get a Combo Drive from a retailer, and connect via FireWire, that way the DVD is mounted on your desktop and you can use Apple's DVD Player to view. You can also burn CD's or DVD's if you get a DVD burner

Odd that your PowerMac G4 500 doesn't have a DVD drive. It must be custom because (I thought) all of the PowerMacs (AGP Graphics) of which I have one at my office came with DVD, standard. Perhaps it's the newer PowerMac 533 (Digital Audio) which came with CDRW. Wish I could help with your dilemma.