The type of RAM you should get depends on the motherboard you plan to get. Some 775 boards are designed for DDR2 RAM and some are designed for DDR3 RAM. If you plan to use a 32-bit OS, you could get by with 2x1GB sticks of RAM because 32-bit windows cannot see or use more than ~3.5GB of RAM. If you are using a 64-bit OS, you can get good performance from 2x2GB sticks. You CAN buy RAM that matches the motherboard's 1333MHz bus, but you don't have to do so, just make sure the RAM you buy is on the Qualified Vendors List for the motherboard you are getting. Most motherboard mfrs post the QVL for their motherboards on their websites.