To run 32-bit software in 64-bit operating environment, you may need a 64-bit emulation to run the 32-bit soft within, and depending on unpredictable conditions you may experience performance degradation doing so. I suggest you make sure all your software needs are certified 64-bit before making the jump. And such a jump today means you'll be confined to a limited amount of software.
32-bit architechture limits the RAM usage to 3,26 gb RAM for each application. But with 64-bit, yes, each application can use tons more RAM - whatever RAM is left after the amount the operating system uses (which is usually 300-800 mb).
"Listen through the equipment, not to the equipment"
- Bill Putnam