A feature of ALL PowerMacs have been dual monitor support. It has been this way for quite some time now, including all PMG5's and many G4's before them.
Reading the thread, I think a couple fo things are lost in translation, but you are on teh right track with that adapter if you intend to run dual DVI displays. As Apple phased out of ADC displays, the newer cards are dual DVI. Regardless, these models also came with DVI to VGA adapters as well. Short of an adapter, you should be set with duals, no matter what their input (DVI, ADC or VGA).
In addition, as someone else pointed out, you can run these dual displays at independent resolutions. The control panel will pick up the presence of the monitr and you can adjust resoltuion and virtual configuration there.
Hope that helps,
keytohwy
We're talking about a Powermac G5 and not an iMac G5 right?
Powermac G5