Microsoft has an excellent Q&A about Windows XP Professional x64, at: 
http://www.microsoft.com/windowsxp/using/64bit/russell_x64faq.mspx

                                 ***

Microsoft(r) Windows XP Professional x64 Edition is a special version of 
the operating system that will only work on the following processors: 

AMD Athlon 64
AMD Athlon 64 FX
AMD Mobile Athlon 64
AMD Turion 64
AMD Opteron
Intel Xeon EM64T
Intel Pentium 4 EM64T

Intel Itanium and Centrino processors are not supported in Windows XP Pro x64.

                                 ***

64 Bit Technology was first introduced in higher-end systems such as the Intel
Xeon and AMD Opteron servers etc. The 64-bit architecture is just beginning to
find its way into consumer-oriented PCs. Manufacturers and Developers are
working on delivering 64 Bit Drivers, which appears to be the way of the
future, as we went from 16-bit to 32-bit and now 64-bit. 

At present, few Consumer level Software products support the 64 bit OS. 
At a certain point, not far in the future, this new Technology will become
mainstream, and Turtle Beach will make 64-bit Drivers available for current
products. 

                                 ***

More detailed info for the new "x64" platform: 
(AMD Athlon 64, Intel EM64T and Microsoft Windows XP Pro x64 Edition): 
----------------------------------------------------------------------

In late 2005, Microsoft released its new 64-bit version of Windows XP, called
"Windows XP Professional x64 Edition." This operating system was designed
especially for the AMD Athlon 64 processor and Intel's subsequently released
and similar product, the Pentium 4 EM64T. 

Microsoft, AMD and Intel are quick to point out the undeniable advantages of 
a 64-bit platform that can run 32-bit programs natively. However, it is not 
as well known that 32-bit device drivers cannot be used in this platform. 
In other words, manufacturers of peripherals MUST provide all-new 64-bit 
drivers for their products in order for them to be usable in the x64 
platform.

Of course, the hardware manufacturers are under a lot of pressure to provide
instant support for the x64 platform. While this would be great, it is really
not possible. The situation is similar to that faced around 1997-98, with the
fully 32-bit Windows NT 4.0 being touted as the future replacement for Windows
95 and 98, which were hybrid 16/32-bit operating systems. Windows NT 4.0
required brand-new 32-bit drivers for all peripherals. Windows 9x drivers
would not work. 

It took until the introduction of Windows XP (based on NT Architecture but 
using the new WDM technology) in early 2002 for true Plug-n-Play driver
support for consumer multimedia peripherals in 32-bit Windows. Hopefully it 
will not take quite that long for the migration from 32-bit to 64-bit Windows.

In the meantime, Turtle Beach, like many other peripherals manufacturers, 
is just beginning its work on 64-bit driver support, as resources and
financial constraints permit. Please bear in mind that the current state of 
the PC world is that the vast majority of computers for "casual home users"
will be running 32-bit Windows on 32-bit hardware, for some time to come. 
Just as happened about over the last 10 years, the point of critical mass 
will eventually be reached, and we'll all begin the journey to a 64-bit 
future. Just not right this instant. 
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