This all depends on your CPU. 64bit Vista will give you let you go over 4GB ram. For 32bit you cannot go over 4GB. Most programs are written in 32-bit so performance wont really matter until more 64bit apps come out. 64bit Vista runs a bit faster than 32 because the code is optimized. Most new processors coming out are 64-bit native and are running 32-bit in a compatibility mode. The next Windows is rumored to require 64-bit processor. If you use Windows Vista 64-bit you will probably never have any problems with 32-bit programs but you need to make sure that 64bit drivers are available for your accessories. So far most companies have been good with this. When XP 64 was released very few companies supported it