Rule #1--don't listen to matty.
Okay, here's the breakdown. I'm going to tell you not to go with Gigabyte but NOT BECAUSE OF WHAT MATTY SAID. Gigabyte is a fine producer of motherboards, they just are not for overclocking in any way shape or form. You, going to game, should look for something that will be overclocking friendly. I suggest Asus, ABit, or Chaintech. These three brands are the ones you're going for.
Chipset--well this largely depends. If you're going for Athlon XP (at this point we're going to say you're going AMD since it is by far the best gaming chip with the best bang for buck) then you'll want nForce2, a great chipset. If you're going AMD 64, however, you'll want VIA, as nForce3's have been having problems. This is also considering you're going AGP and not PCI-Express, which is PCI-E, the successor to AGP.
I suggest, however, you go PCI-E, dual PCI-E in fact, with two slots for nVidia SLI (Though ATi's new cards with the dual core may stack up well against SLI) and in that case, you should go nForce4, the newest of chipsets.
Chips. AMD of course, but which? If you're going Athlon XP, I suggest a chip anywhere from 2500+, 3000+, but make sure it is a barton core. Also, for everything here, shop [url=www.newegg.com]newegg[/url]. Best prices, fast shipping, awesome customer service. If you're going AMD 64, I suggest the 3200+ simply because of the change in cache and core--it gives it a bigger advantage over the 3000+ than is usual. Also, I forgot to mention this in the motherboards section, if you're going AMD64 MAKE SURE YOU GET A SOCKET 939 BOARD. If you go dual PCI-E slots, and go with the nForce4 chipset, no worries, that's already Socket 939.
Alright, that's about it. For the best performance, I suggest an Asus, Abit, or Chaintech board from newegg.com, Socket 939, nForce4 if you can find it. Chips I suggest the 3200+ socket 939 version.
WHATEVER YOU DO STAY AWAY FROM MSI LIKE THE PLAGUE. They are a HORRIBLE board manufacturer, with shoddy parts, and horrible customer service. Once you get all this stuff, post again, and we'll talk about overclocking
