There an Adapter
I don't know if this works with the dualcore G5s, but it works with the previous models and with the Mac mini.
"Apple DVI to Video Adapter
Use the DVI to Video Adapter to connect the DVI port on Power Mac G5 or Mac mini to any S-video or Composite enabled device.
Price: $19.00"
"The Apple DVI to Video Adapter was designed specifically to allow Mac mini and Power Mac G5 systems users to connect from the DVI port to S-video or Composite video devices such as TVs, VCRs, or overhead projectors with S-Video or RCA (Composite) connectors. The Apple DVI to Video Adapter is designed to work with the DVI port on the Mac mini and Power Mac G5 systems only.
Use a separate DVI to VGA Adapter for VGA video out for Mac mini or Power Mac G5 (included with all Mac mini or Power Mac G5 systems or available for order as a standalone kit).
Important:
Requires Mac mini or Power Mac G5 with DVI port."
Good Luck