I've just finished an interesting article here, which details AMD's plans to extend the x86 ISA to 64 bits.
Without getting too technical, the article does give a quick and easy breakdown on exactly why a 64-bit x86 processor would be better, why it can address more RAM than a 32bit chip, why 64 bits and what exactly a 64-bit processor is, anyway.
Some interesting points are the revisions underway concerning the number and width of registers, and in how memory is addressed. The article also explains how it is possible to run legacy 32-bit code on a 64-bit processor, why you need a 64-bit operating system to make the best of one, and how it will still be possible to run a 32-bit operating system like the one you are no doubt using now on such a processor.
Its a matter of differing opinion between Intel and AMD exactly how greatly a 64-bit platform would be adopted in the desktop market, but the article has much to say on Epic Games's Unreal engine guru Tim Sweeny's views on such matters, particularly in the area of gaming.
"We're going to ship the 64-bit version of UT2003 at or before the consumer Athlon64 launch. And our next-generation engine won't just support 64-bit, but will basically REQUIRE it on the content-authoring side."
A good read, here.