I finally upgraded my Dell Dimension E520 from the 32-bit version of XP Professional to the 64-bit version. I had to use 32-bit network and sound drivers, but I did find 64-bit graphics drivers for my Radeon X1300 graphics card. After some poking around on the Brother website, I did find working (32-bit) drivers for my Brother HL-2070N printer. In fact, the only device that I am no longer able to use is my Canon CanoScan 3000 ex scanner. I tried to run the scanner in a VM in VMware Server, but it blue-screens the VM.
Attempting to install the Roxio CD/DVD writing software resulted in an unbootable computer, until I reinstalled the software without "Roxio DLA". I've never benefited from "DLA", which attempts to make a CD/DVD writer work like a floppy disk.
I still use Quicken 98 as a checkbook register, and it refused to install in XP x64. Fortunately it runs well in a VMware VM.
When I run the Task Manager, I can see that about 1/2 of the processes are still 32-bit, including Microsoft Visual Studio 2008 SP1. At least my .NET programs run in 64-bit mode, plus I did find a 64-bit version of 7-zip. Given the fact that mainstream machines are being sold with 64-bit Windows operating systems, I'm a little disappointed at the slow uptake of 64-bit. At least the 32-bit programs work well, plus I'm now able to use all my 4 GB of RAM.