If you will use win xp and planning of buying 8GB ram you have to have xp x64 coz win xp x32 will anly see 3gb of RAM. x64 architecture is a bit faster and more advance. Programs like max, photoshop will benefit from it and will give you better performance etc. And with the question of choosing an operating system i just feel more comfortable using xp but that is just my preference, new vista OSs are more advanced but im fine with Xp and i dont see changing that. As far as i know you cant run max 9 x64 on vista but i could be wrong.