Dual Core CPU`s require an OS that supports dual core, Windows XP and 2k do by default. They also require Bios support, which should only be a bios update if needed.

Programs would need to be written to support mutli-core to get the best out of them.

However programs written in single-core should see some improvement as 1 core will only run the App in question and the other core would be running the OS.

I would personally not bother with a laptop for any type for 3d work. Its a fact that any laptop processor runs slower that its desktop counterpart.

If you must go laptop I'd wait. It won't be long before we start seeing AMD64 X2 mobiles !