OP, If you need help with this, i'd be glad to help you pick parts for your build. The biggest thing is to make sure things work together. If the mobo only has SATA drive connectors, a IDE hard drive will not work. You have to make sure the memory will work with the mobo you have picked too. Mobo, CPU and memory certainly are critical to work together.
If you want help, let me know. I'm sure others will chime in too. Dale :-) :-) -- I am only responsible for what I said ... Not for what you understood or how you interpreted my words!