Windows 7 Forums have published brief but interesting article which helps explain the pros and cons between 64 bit and 32 bit versions of Windows 7. Here's an excerpt:

Pros and Cons of a 64 bit system:

* You can address much more than 4GB of memory, which is ideal for avid gamers, CAD, video editors and heavy multi-taskers. However, any 32 bit software you use will still be restricted to 4GB memory – you need a 64 bit CPU, OS and applications to take full advantage of the extra RAM.

* 16 bit applications will no longer run. Although this is unlikely to be a problem, if you use very old software (from the Windows 3.1 days!) then it will not work under a 64 bit OS.

* Existing 32 bit drivers no longer work.If you have older or poorly supported hardware you may find that it can no longer be used. Got a 7 year old scanner that just about works in Vista? You may not be able to get it working in 64 bit Windows 7.

* Unsigned kernel-mode drivers no longer work. Along with the issue above, the inability to run unsigned kernel mode drivers will cause problems for old hardware. (There is reportedly a way to bypass this check).

* Running some 32 bit applications on a 64 bit OS could actually be slower. The additional overheads in running 32 bit software in 64 bit mode could cause a slight degradation in performance. It will take some time for 64 bit software to become the norm.

The conclusion? Well, it depends on what you use your system for. If you have a 64 bit capable CPU but use older hardware, it would be safe to stay with a 32 bit version for the time being to ensure that you don't need extra upgrades. If you've got the latest hardware and drivers are available, then it may be worth while taking the step up to a 64 bit OS. If you regularly work with resource hungry applications that are 64 bit optimised (such as video editing, CAD and image packages) then it would be especially beneficial to be able to work with over 4GB of RAM amongst the other improvements.