What is x86 and x64? What is 32-bit and 64-bit Computing?

X86 is 32 bit and x86_64 (or just x64) is 64 bit.

If you're doing normal browsing/playback/typing stuff, you won't see any difference between 32- and 64-bit. This only comes into play when you're moving huge amounts of data, like video editing or audio mastering.

32-bit vs 64-bit Computing
64-bit is still relatively new on the desktop/laptop scene, and the drivers for Windows 64-bit Edition are less than mature. You will run into problems. I would stick with Windows 32-bit for stability, even if you have a 64-bit processor. I would suggest you hold off on 64-bit Windows until Windows 7 is released; hopefully hardware vendors will write stable drivers by then.

The 'data buss' is used to move the data around inside your computer. In a 32-bit computer, the width (or size) of the data buss is 32-bits wide. A 64-bit buss is twice as wide so the system can move twice as much data around. Being able to process more data means a faster system -- but only for specific things. Normal office productivity and web surfing will show no advantages at all, whereas graphics processing and scientific calculations will go much faster.

Windows 64-bit system
It has been reported that Vista 64-bit, Microsoft's next Windows release, already has severe problems. It already has had critical updates applied, prior to release. Nothing like getting a head start, is there. Other problems with 64-bit is the general lack of stable software to run on these Ferrari of the computer world. The entire system has to be designed and built for the wider data buss, too, so the system will cost more. On the contrary, most 32-bit software will run on a 64-bit system, but that causes one to wonder why one spent the money in the first place.

Who needs 64-bit system?
Mostly businesses, universities, scientific groups, and government. If you produce videos, computer art, or develop programs, 64-bit systems will be helpful. But for the home user, 64-bit is currently a bit overkill. You won't see faster activities like writing, spreadsheet processing, or web browsing so (in my opinion), save your cash for something else (like a bigger hard drive or more RAM).