Most programs designed for the 32-bit version of Windows will work on the 64-bit version of Windows. Notable exceptions are many antivirus programs.
Device drivers designed for 32-bit versions of Windows won't work on computers running a 64-bit version of Windows. If you're trying to install a printer or other device that only has 32-bit drivers available, it won't work correctly on a 64-bit version of Windows. If you are unsure whether there is a 64-bit driver available for your device, go online to the Windows Vista Compatibility Center.