What video card do you have?
I'm using a 6800 Ultra, which has dual DVI outs. I just have a DVI-HDMI cable running from the computer to my TV. HDMI and DVI use the same signal protocol-the difference is that HDMI-obviously-uses a different connector and also supports sound. Thus, the cable is passive.
All G5 Cards(or at least the Mac edition ones) I'm aware of have either dual DVI or DVI+ADC. ADC is really DVI with extra connectors for power and USB, so again a passive adapter can be used to turn an ADC port into a DVI port. Then, run a DVI-HDMI cable to your TV.