With the right video card, it's no problem. Apple sold monitors(or I guess a monitor) along side the G5 with higher resolutions than that. You will need a card with a dual link port to do it.
Offhand, here are your GPU options if you have an AGP PowerMac
Radeon 9600 Pro PC&Mac
Radeon 9650XT
Radeon 9800
Geforce 6800 Ultra(2xDL-DVI)
Radeon X800XT
Radeon X850XT
There are also plenty of flashed cards that can do it, although others will have to give you the specifics.
All cards that shipped with the PCIe G5s have at least one DL-DVI port. If you want to drive two of these monitors, you need either a Quadro FX4500 or a Radeon X1900.