Nope, but for the card you can always try eBay for one of the Orange Micro Cards.
Though that is likely to be pathetically slow.
That type of thing bombed in the first generation PowerMacs, and got killed soon after by Virtual PC and Softwindows.
Anyway what you are asking for is best served by a complete $499 Dell system, which would turn out faster and cheaper than any card. Just load XP Pro on it and you'd be able to run a Remote Desktop Client.
PCI-X doesn't have the bandwith that a front-side bus does, and none of the Intel board chips would exist on the PowerPC board.
Not happening, and frankly unnecessary, as when the G5's stop being spiffy, the Intel processors will be so far ahead that sticking into your G5, especially on a PCI-E/X bus, would cripple it beyond words.
The only instance I have heard of a PCI processor is Sonnet's upgrade for the PowerMac 7200.
How would a processor on the 33MHz PCI bus (or 133MHz on PCI-X) communicate effectively with a 1GHz motherboard on a G5?
The 7200 had a 50MHz bus so it wasn't that bad, but this sort of thing is just impossible with today's Macs
A x86 compatibility board is more possible. Highly unlikely, but more possible.