Hey men, I'm 14 two and built my computer. What you may want to buy is: if you use intel and Nvidia:
Gigabyte GA-8NSLI Royal, it's the one I got and was awarded: Best overclocking capabilites, with nVidia Nforce 4 SLI North Bridge, you can run SLI with your GPUs and it's not that expensive, 187$ I payed on Newegg.
Now if you overclock, this is the ways you should do.
First, on the GA-8NSLI Royal, the multiplicator is blocked (due to socket 775 I think) because Intel blocked it. But your way to overclock is just going to be easy, under the BIOS, find the section where it says FSB speed, it's at 800, to overclock, set the thing to expert, not linked (cause your DDRAM will overclock with your CPU and may not boot correctly). Now, add 10 to 800= 810, reboot, check if it boots correctly, then you may have a freeze while loading windows, this means that you need to get the VCore on rank up VCore SHOULD NEVER BE MORE THAN 1.525 OR SO. The Voltage should almost stay on normal until you face a freeze. My CPU is a Intel Inside Pentium 4 HT 64-bit support (650) at 3,4 GHz, to go up to 3,8 GHz, I changed the FSB from 800 to 896 and it's like 3,81 GHz. BUT REMEMBER OVERCLOCK LITTLE BY LITTLE. Remember that your DDRAM CAS Latency isn't above 4 because then overclocking won't work out good.