1) Yes
2) Kinda. The problem is that the with x86 and boards which do not have the ability to map addresses >4G, they will map their hardware addresses starting at 4G on down until it is satisified (so this means addresses for the BIOS, any video card memory, etc.). Windows XP/Vista, as of XP SP2 x86, is then further artifically limited to addressing 3.5GB of physical memory. Of course, unless you have very little hardware, you may not get that much due to the first issue with the BIOS mapping addresses in the 4G range. I was able to get 3.5GB by setting my AGP aperature to 64MB (I had a GeForce 6800GT 256MB, IIRC).
I'm running Vista x64 w/ 8GB RAM now, though
