Well, what do you want to do with it? If you're running a 32-bit OS and playing older games like Halo and Source-based games, then 2GB is fine. If you plan on Crysis and its sequel, or Far Cry 2, or what have you, you want 2x2GB. If you get just 2GB, I suggest getting a 2x1GB kit, since that will double your memory throughput (two sticks operating has more bandwidth than one).