A little Help with a New Computer

Hi, I've been researching computer components for awhile and I figured that the best way to figure out what I need is to ask the all knowledgable Tom's Hardware Community  

Anyways, I already have the hard drives, cd-roms, graphics card, good sound card, lan card but what I still need to get is the CPU, Motherboard and RAM. I'm sort of on a budget, roughly $400 but I usually tend to go over my budget and I'm not too worried about getting too little RAM since thats the easiest thing to upgrade later. Anyways, what I'm thinking of getting is a Pentium 4 2.4 ghz processor ($210) and I've been looking at the Gigabyte 8inxp since I've heard nothing but good things about it but that already takes basicly all of my money. What I was wondering though is what the huge difference was between that mobo and the 8SG667 which is less than half its price.. Right now I'm trying to decide between those two and I figured if there is something better out there you guys would let me know. Anyways if I go with the first option that leaves me with getting cheap DDR Ram until I get a chance to upgrade it but with the latter board I can get something decent to start out with.

Thanks in advance for any help,
Brian