GF5600 is PCI-only.
The 5600 were originally released as AGPs only, but some models were updated to include an AGP to PCI-E bridge, see this from Wikipedia on the FX series:
The GeForce FX line moved to PCI Express in early 2004 with a number of models, including the PCX 5300, PCX 5750, PCX 5900 and PCX 5950. These cards were largely the same as their AGP predecessors with similar model numbers. To operate on the PCIe bus, an AGP-to-PCIe "HSI bridge" chip on the video card converted the PCIe signals into AGP signals for the GPU."