I think I have an iMac G5 - flat screen, white covering. Right now I have OS X 10.5.8 & it's running rather slow. The processor is 2 GHz Intel Core Duo, Memory 512 MB 667 MHz DDR2 SDRAM. I want to upgrade to Snow Leopard 10.6.3 - tried today but says I don't have enough memory. How do I get more memory & what do I need to do it. Thank you for any help!