tacit has answered your last question and I will take a shot at the second. Applications have to be written to run in 32 bit mode, 64 bit mode, or either. Do a Get Info (Command+I) on an application and if there is a 32 or 64 bit checkbox it can run in either mode. otherwise in current applications it is safe to assume they are written for 64 bit operation. You Macbook Pro has Core 2 Duo processor and a native 64 bit architecture so there is no advantage to running in 32 bit mode. The performance, particularly OS performance, will be greater in 64 bit mode. You are literally processing twice as much data with each CPU cycle.
By the way, it would be helpful if you would add your OS version to the system description in your signature.
