RAM is another word for the memory, and has nothing to do with how many programs are loaded (that's hard drive space). You definitely won't have a particularly good experience with only 512MB, that's the minimum we recommend for WinXP. You don't actually need the Aero interface, and Win7 will just disable that if it doesn't find adequate hardware. However, it sounds like you have quite an old PC there, and you may be a bit disappointed in how Win7 runs on it. I've got to be honest, I wouldn't install Win7 on WinXP spec hardware myself.