The TonyMacX86 site has all the info you're going to need.
Basically you're going to want purchase a retail DVD of MacOS X if you haven't already - keeps you as legit as you can get on a hackintosh.
You're going to build a USB boot loader. Such as Chameleon 123 / iBoot. You may need multibeast. Obviously you'll need another PC with DVD to Build the image to USB.
I think anyone who's made one will tell you that they're not all that exciting for the work involved in getting it up and running properly. Better off playing with the underpinnings of something like the SteamOS or Ubuntu if you don't want to put Windows on there. If you're going for a HTPC you may want to try XMBC.
I had one before TonyMacX86 came out, it worked well enough for the purpose. However, it was discovered that the later version just rip off what's online already and sell it to you for $100+. Go with TonyMac and build according to their hardware list and you should be fine. I'm running MutliBeast with a Gigabyte 775 board and Nvidia 9800GT.
EDIT: There're thread for BRIX already on TonyMacX86, just have to search for it. In regards to the wireless card, there are cards that work straight out of the box.