AGP or PCI

Im a bit confused about replacing my graphics card. Do they go in the AGP or PCI slot. Is there a list of compatible graphics card for a older G5? I was looking at the Ati Radeon 9800 Pro VGA AGP 8x 128MB For Mac Edition. Im guessing from the AGP in the name thats where it goes? It a bit confusing as to what card will work with what Mac and where they go. I have model M9454LL/A, 1.8 DP (PCI)

You have it correct on all counts. You can have one video in the AGP and another supporting a second monitor in the PCI slots. The 9800 AGP is a correct model but it MUST be the Mac version to go in the AGP slot.