Is 64 bit mode for something else, video editing or something?
Very basic explanation: For an application to run in 64bit mode, you need three things:
1) A CPU that can execute 64bit instructions. Most of them do now.
2) An operating system that is 64bit capable. With Windows 7 64, you can tick that one as well.
3) The application itself needs to be written to support 64bit. This one is the major problem, since 99% of apps are still coded with 32bit instructions. There are no 64bit games out there, and very few 64 bit applications.
The only advantage 64bit computing gives you at this point, is that you can break the 32bit barrier of 4GB of RAM.