yes, 64bit processors can break the 4gb memory limit, through increased memory address reading... however, as noted above, the max amount of memory is dependant on the combination of hardware pieces... big limiting factor is the number of memory slots, usually 2 in laptops. Then how much memory can be fitted per memory slot. usually 512mb or 1GB, in your case its 512mb...

The hardware manufacturer puts these limits, the software (OS, like XP/VISTA) have capacity and capabilities to support more than 4GB, hence the help & support says so