I purchased a Power Mac G5 Quad on e-bay and have ordered a WiFi/Bluetooth board from an on-line vendor. My question is if the installation is straightforward. Will Leopard recognize the board and have drivers or will I have to download and configure? Any gotchas that anyone has run into? Apple states this is not a DIY add in, but I'm not sure why with the bulit in WiFi antenna, should be a simple hook up.

Thanks for your help

Yes, Leopard will recognize and use both Bluetooth and Airport.
There's two antenna connections - which can be attached to either connector on the card.

Problems can happen if one (or both) of the antenna wires slip behind the logic board. I had one where I had to pull out the logic board to retrieve a lost wire. That's not a simple task. Hopefully, both of your wireless connectors are still clipped in place, and easy to get at.
Do you know that Airport Extreme/Bluetooth combo card does not plug directly into the logic board, and requires a secondary card, known as a "runway card", as an adapter for the wireless card?
The little plastic rivets that hold that runway card in position sometimes are missing...
Hopefully, the runway card is either already in place, inside your G5, or is included with the combo wireless card that you ordered.

Thanks for the quick response. Did not know about the runway card. So once I get it installed properly, Leopard will configure automatically. That makes it fairly easy.

I don't think I would make that leap.

Your OS X system should detect the Airport card.
Although you don't need to install any software, the system software might not be completely installed, or may have the wireless card turned OFF by default, so you may need to enable the card, which can be done easily from the Airport menu, which should show up as another indication that the system is installed properly.
And, eventually, you would be subject to whatever authentication you have to connect to your wireless network.
But, yes, fairly easy - and may even seem 'automatic', as you say.
I prefer the term "automagic", but, like a lot of other old-time Macers, I just expect it to work.

A quick Google search turned up the Apple document AirPort Extreme Card Replacement Instructions (http://manuals.info.apple.com/en/airport_card.pdf).

Unfortunately, the instructions that you found will not help the OP in any way to install an Airport card in a Quad G5.
There's at least 3 completely different Airport card installs in the PowerMac G5, depending on the model. That link does not represent anything in the OP's model, but then, you didn't know that there are several possible installs.
The OP has a G5 Quad, known as a Late 2005 model, and is quite different internally from other PowerMac G5s. (Even the power cord is different, and not usable on anything else) It does not use an Airport Extreme card, per se, but mounts a Wifi-Bluetooth combo card on a daughter card, which in turn, plugs into the logic board.

I did contact the vendor and they confirmed the inclusion of the runway board and that the board I purchased was in fact the kit for Quad G5, Late 2005. THe only part number they had listed as 922-7152.

Sounds good!
Just though I needed to ask, as I read about folks in your situation that don't research quite enough - and end up with a wrong part.

You'll more than likely need to get the screw on external antenna also otherwise the signal range is going to be lousy.

The Quad doesn't have an external wireless access.

If you find that you need better reception, then an external antenna would connect directly from the card.