OK, thanks.
That is actually an original Mac Pro, not a Power Mac G5. It would have one of the following graphics cards:
NVIDIA GeForce 7300 GT, GeForce 8800 GT, Quadro FX 4500, or ATI Radeon X1900 XT
All of those cards have DVI ports, so the adapter I mentioned should work just fine. I am actually using an Apple DVI to ADC Adapter with my old 22" Apple Cinema Display connected to a 2007 MBP's DVI port.
C