Okay, so how did you test that the ram works fine? I suggest getting hirens boot cd and running memtest for an hour or so.
Your second issue is because windows xp uses specific drivers from your old motherboard/cpu during its startup. You will have to at least repair your OS. I suggest switching over to windows 7, windows xp is somewhat outdated.
To test the ram, I just used the RAM test button on the motherboard.
And damn, I'll need to upgrade either way, I never had a boot disk for XP.