64 bit takes advantage of the extra processing power in every clock cycle of a 64 bit processor. 32 bit you'd be wasting it. supporting the processor in 64 bit is easy, question is does the rest of the hardware in the laptop have 64 bit compatible drivers?
thoroughly check this before you install 64 bit, you might get it to boot, but certain other things (like wireless) might not work under 64 bit vista.