I have read many threads about using Vista 64 on a Mac Pro, especially with > 2 GB RAM. My question is what is the downside of using the 64 bits version? Are some older apps incompatible? Will some games not work properly? I have Mac Pro (8 x 2.8) with GeForce 8800 GT, and 4 GB RAM. I use Boot Camp mainly for gaming, and I just want to find out if it is worth getting the 64 bits version of Vista Ultimate, instead of my 32 bits Vista Ultimate. Does anyone know of incompatibility issues with older (DirectX 9c) games?