what is the best cpu and mobo i can get for around 400$? where (links please)

Best for what? If you are assuming the cost difference is only in those two items then you need to rethink. DDR3 motherboards will require new RAM and it is more expensive than DDR2. You may need to purchase a new PSU (power supply). In short, you need to set a budget for a complete computer and select a balanced set of hardware components. This should be dependent on what the rig will be used for.

You can easily buy a decent CPU/board combo for about 1/2 that much. But if you have your heart set on spending $400, we'd need to know if you prefer AMD or Intel & whether you want a dual or quad core CPU. The primary use of the system would be helpful...if it's for gaming, is running two video cards (SLi or Crossfire) a possibility? Do you plan on overclocking? Do you want a full size ATX board or will an mATX board do? How about memory slots - 2 or 4?

Also, do you want to go with the new core I7 Intel cpu ? In that case you'll need DDR3 RAM, which, as OtheHill noted, is more expensive.

the only thing i want is new cpu and mobo, i want to use ddr2 ram i have 4gb already 800mhz also i have that much to spend, and i want the best one for gaming. i prefer intel but if amd is better than just tell me which one to get

You're going to waste $400 (yes, WASTE) because you can't play one stinking game to your liking? And an online game no less? http://www.computing.net/answers/ha... I noticed you neglected to list the motherboard & PSU in your spec list.

well i want a quad core cpu i want the fastest computer poss, now anyways does anyone know or should i just give up, all im asking is a recomendation.