There are a lot more options in most BIOS's that affect PnP, AGP etc than that, sadly.
The FX5200 should be AGP4x so those settings look ok. The 'version' is going to be the ABit BIOS version, check on the ABit site to make sure it's the latest version (if they provide any BIOS updates at all).
I think the FX5200 is newer than XP, so I wouldn't expect XP to detect anything useful about it ("PCI compatible VGA adapter" is all I'd expect). XP only detects devices it has a driver for, and/or has been fed an INF file for at some point.
I'm very much inclined to think this problem is lower-level than the OS. BIOS, motherboard I'm thinking.
That is, if you've removed all possible obstacles (AV is a bit of a thin one, but worthwhile as a desperate measure, anything like multiple desktop manager type stuff, upgrade DX to the latest version, what motherboard drivers have you got installed, etc).