I presume you are referring to the PC CHIPS P53G, which I happen to be using. I also have a Foxconn P4M9007MB with the same P4M900 chipset. Back in December 2008, I tested the following PCI Express x16 cards on both motherboards (using latest BIOS):
GeForce 8400GS (PCI-E 1.0)
GeForce 9400GT (PCI-E 2.0)
Radeon HD 3650 (PCI-E 2.0)
All cards were stable and completed several passes of 3DMark 2003 and 2005, but the Radeon HD 3650 seems to be under-performing by at least 20% on
both P4M900 boards, using Catalyst 8.10 and 8.11 drivers. Radeon HD 3650 should out-perform 9400GT by a safe margin but consistently scored on-par with or lower than 9400GT.
I don't know whether it is an ATI driver problem, a chipset problem, or what. I suppose it is possible the single-core Celeron D that I used is impacting the ATI card more than the NVIDIA card (comparative benchmarks I checked used fairly high-end dual core processors), but that explanation doesn't sit well with me. I am currently running Radeon X1650 PRO without any issues but I haven't benchmarked it and don't run 3D apps that would be demanding enough to expose any performance issues.
I would recommend GeForce 8500GT or 9400GT (which have similar performance), either of which can be found under $40.00. Or if you really need to save another $10, this:
http://www.newegg.com/Product/...x?Item=N82E16814500025
If you haven't purchased the motherboard yet, you might look for something similarly "cheapo" with a different chipset, such as Intel 945GC, Intel G31, or GeForce 7050. All have the same or slightly better specs than VIA P4M900 but with less of the weirdness that VIA's PCI Express and SATA implementation has shown (repeatedly).