I've been thinking about upgrading my RAM. Currently it's at 2GB, and i'm thinking about bumping up to 4GB. It actually says that it has 2.5GB but only 2 is available. What is that about? My motherboard is an ASUS M3N78-EM. I have two empty slots for RAM. Supposedly it can handle up to 8GB of DDR2 1066. What's the difference between 1066 and 800? Why does my load screen say that it's 2.0 ghz when it's supposed to be 3.2 ghz?