You would at LEAST need a 2.8 GHz or above dual core for a GTX 280 to even be worth buying for your computer, and it would have to be AM2 or AM2+ compatible for it to work with your current motherboard. Although, if you were planning on getting a graphics card that powerful it would be a MUCH better idea to go with a quad core processor, which would most likely require you to buy a new motherboard because you probably bought the cheapest AMD motherboard you could find and it probably wouldn't be able to support a CPU that has a TDP higher then 65 watts (uses more then 65 watts of power). Also since you bought the cheapest parts for your computer you would most likely need a new power supply because you most likely bought some stuff cheap one or you are using a stuff one that came with the case. Also in terms of price/performance, a ATI Radeon 5870 costs about the same as a GTX 280 and performs 30% better then the GTX 280. It would be a much better buy if you get enough money to get a new processor and graphics card. Also where are you buying your computer parts from? Because wherever your getting them from really should tell you how many cores a processor has, although if you really knew anything about computers you would know how many cores the processor had by the name.
Ok rundown of CPU cores by name, bold indicates number of cores. This really should not have been confusing anyways... Also, I'm only listing not crappy processor series just in case you get confused...
Dual cores
AMD Athlon 64 X2
AMD Athlon II x2 (Based on the Phenon II architecture, good price for the money)
AMD Phenom II x2
Intel Core2Extreme ( some are dual core, some quad)
Intel Core2Duo
Intel Core2
Triple Cores Only AMD makes triple core processors, but I would not recommend using one with a GTX 280 or Radeon 5870 because the triple cores are made from Quad cores that had one defective core and had the defective core disabled
AMD Phenom x3
AMD Phenom II x3
*Note both Athlon II x2/x3, Phenom x3, Phenom II x2/x3 were all quad cores but had defective cores and had either 1 or 2 cores disabled. They also usually have low clock speeds and would be undesirable for a computer that is going to be paired with a high end graphics card.
Quad Cores
AMD Phenom X4 (Old, slow, Phenoms replaced by the Phenom II line of processors)
AMD Athlon II x4 (Same as Phenom II processors, but with NO L3 Cache and lower clock speeds)
AMD Phenom II X4 (Best AMD quad cores)
Intel Core2Extreme
Intel Core2Quad (Older, but still on par with AMD Phenom II even though they are AMD's latest)
Intel Corei5 (All quad now, dual versions coming Q1 2010)
Intel Corei7 (All quad now, dual versions coming Q1 2010, very expensive)
Core i7Extreme Edition (You cannot afford this, its about $1000)
For you, I dont think you could afford an Intel Corei7 because you would need new ram as well as a new inel motherboard, which would be much more expensive then a new AMD motherboard. Basically, if you are looking to spend a large amount of money, go with either a Intel Corei5 processor (because you can use the same ram with Corei5's) or Phenom II. If you have little money, go with a good Intel Core2Duo or an Athlon II x4.
