Is there any real advantage to 64-bit Windows XP
For most people there isn't much of an advantage. 64-bit Windows XP has proven to be a life saver for me because of the larger amount of RAM it will address.
32-bit operating systems will only address up to 4 GB of memory (physical RAM or virtual memory). This includes the Windows kernel (core). Any application in Windows 32-bit can only use up to 2 GB (3 GB with a special switch enabled in boot.ini) and the other 2GB / 1GB is reserved for the Windows kernel. This means that any one application can ONLY access up to a maximum of 2 GB of memory address space (3GB with the switch, which can affect stability in some applications). Once you reach this limit, you instantly start getting "out of memory" errors, regardless of how much RAM you have installed. Windows won't see it.
In 64-bit, this 4GB total cap is increased to 128GB (in reality. The theoretical number is much MUCH higher than 128 GB. I think it's somewhere in the EB range

). Using the standard 2GB for the operating system, that leaves 126GB of virtual and physical memory address space for applications. For my audio work, I can Very Easily fill 3 GB of memory so this is a tremendous advantage for me. To put it in perspective how fast I can fill up RAM, this "Things Change" project takes up almost 2 GB of RAM when it's loaded...it's only about 33% complete and it's a relatively light project. I have 4 GB of RAM installed in my 64-bit computer and am considering upgrading to 8 GB in a couple of months when I get more money.
Basically, if you find yourself running out of memory, 64-bit will solve all of your problems. Otherwise, there isn't a huge advantage. For me it's a life saver. For 99% of people, it's not worth the hassle of trying to find drivers that don't exist

I fear that all of my programs and games will not work.
I've never had a problem with programs or games not working. The problems are trying to find 64-bit drivers. Once you find the drivers, all of the applications will work fine. Some devices and companies simply don't have 64-bit drivers for their hardware yet. That's the big problem right now. I was able to find 64-bit drivers for nearly all of my devices though, including:
ATi X1950 Pro video card
Sound Blaster X-Fi sound card
built-in network card
I was Not able to find 64-bit drivers for:
my older network cards
my typing keyboard (my media buttons don't work in x64

)