With XP Home no application will use more than 2GB (though the rest may be used by another application). With XP Pro an application that has been coded to do so may use up to 3GB of RAM if the option is switched on at the OS level. To go beyond 3GB per application you need 64 bit Windows and applications. I'd like a bit more infor on the Poser 6-doesn't-like-2GB issue too, as I'm planning to buy or build a new machine and am aiming for at least that (and 3 if I can afford it).