lol Hold on about the Vista issue, we're trying to get a definative answer on that. I may or may not have been talking based on bad data (i.e.--I was wrong and talking out my ass). If you're working on this for Christmas, though, we'll have an answer for you in time. On our side, we appreciate you providing us with all the relevent info, and taking the time to ask about things before you start, instead of asking us in January after you ran into problems. I hope you enjoy working with the community here, I think we've got some pretty good people. That's certainly been my experience.
Oh, and your kids are lucky. My mom couldn't get why I went and built a new rig this past September to replace my 3-year-old system, and I like to play games that are a lot more demanding than WoW.
As for the mobo, if you're going with a quad core, the X38 chipset would be the choice. Make sure the 8800GT you go with is one of the new G92 cores. Post a link and ask if you're not sure. I recommend EVGA because of the Step-Up program (buy a video card, register, and if you want a higher-end model within 90 days from purchase, just mail in your current one and get the new one for the difference), and because they're a solid manufacturer. Alternatively, the G92'd 8800GTS cards should hit sometime in early to mid December. I'm waiting for one, and they'd better have it.
As for 64-bit vs. 32-bit, the main difference is that 32-bit can only support 3GB of RAM, while 64 can do more. The main cons of 64-bit are: lack of driver support, some games/programs may not run, and driver support for peripherals is somewhat spotty. Furthermore, I have heard that since most games are designed to run natively in a 32-bit environment, running them with 4GB of RAM in 64-bit yields about equal performance to 2GB in a 32-bit (meaning the advantages of more RAM are cancelled out by the non-native environment). I'm sure someone around here had mentioned that, can anyone confirm?
Oh, and if you're only worried about a dead mobo, a direct replacement (same make and model) will work fine, even with the most restrictive license, the kind you'd get if you bought a Dell. They do that so the motherboard can be replaced if it fries.