After reading "alot" of messages, I came to the conclusion that the 5xxx series might be the most modern card supported.
I did alot of searching... Wow, you can't hardly find any of the supported cards on the market! Not even used. There was hardly anything on ebay....
I found several "new' Geforce FX 5200's in PCI and AGP flavors, some as low as $18 USD. However since I'll be using an ASUS A8N-SLI SE for my motherboard, I elected to go with a PCI-e based card instead. In my case, I picked up an "EVGA GeForce PCX5750 128MB PCI Express x16" video card.
I saw in the forums that some 57xx series cards have issues. I hope that is not the case with this one, but if it is, at least I didn't have to give much for it. I picked up a factory reconditioned card from www.newegg.com
for just $25 USD.