How many RAM do you have in this machine? I realized that a 64-bit system is only worth if you have more than 4 GB. Otherwise a 32-bit would be sufficient and would use less memory. Every 64-bit program is larger than a 32-bit software because of the bigger address space. All registers are now doubled in space.

I have Vista 64-bit and when I work with GIMP, Lightwave/Modo and Ureal-Editor at the same time then I exceed the 4 GB RAM (I have 8 GB). But in most of the cases my system uses something between 3-4 GB. So it does not bring a big difference to a 32-bit software.
Even if I paint on 2048x2048 textures with 20 layers in GIMP then the entire system does merely break the 3 GB border. Keep in mind that I use 64-bit software. So a 32-bit system with the same applications running would use only something around 2 GB.

But it can be another story if you want to edit videos.