The biggest benefit to 64 bit is memory handling and all those programs you mentioned benefit from more memory.
If you're buying an "off-the-rack" pc,  get one with four dual channel DDR2 RAM slots, and you can get up to 8 gigs of RAM into it.
Avoid a machine with integrated graphics, as the video card is part of the motherboard and can't be updated, plus it uses system RAM, taking it away from your apps. It's better to have an available PCI-e x16 slot for a good 3rd party video card, and disable the integrated graphics if it has it. Which most of them do.
64 bit XP and Vista are both great operating systems, but in the end it's the hardware that makes the real difference.