ahh... what speed are the 256mbs? what do you plan on doing with your computer... and if gaming, what games? some games dont take alot of memory.
also, ram comes in different speeds. for instance my DDR400 Corsair XMS 2-2-2-5 memory would run faster than DDR400 Corsair XMS 2-3-3-6 memory, and MUCH faster than DDR333 memory. you can use CPU-z to figure out how fast the memory is (the frequency multiplied by two)(mines 200mhz, DDR400)
http://www.cpuid.com/cpuz.php