I use both and never experienced problems. What you have to make sure with for Windows 64-bit for AMD64 Processors, is that your runtimes are up to date.
You also have to make sure you have setup the system correctly.
Default Settings = 32-bit Emulation, which is wrong. You can run 32-bit Applications with 64-bit Extensions, it is one of the compatibility settings in the main programs.
It's there because alot of programs are not yet designed to be Win32+ Compatible. It would be a good idea for TGC to update the DBP Compiler to use MSIL, as this would make it 100% Compatible no matter what Windows and Processor it's put on. TGC haven't really been thinking ahead though.
Windows XP 32-bit however will run with 64-bit Extension provided you install the drivers for your CPU. For compatibility means Athlon64 Processors still use an AthlonXP (32-bit 8086) Core.