OpenChess

... don't work with Windows XP Pro x64 (64-bit).
I tried with both Houdini 1.03a and Houdini 1.03.

I know, Robert Houdart has written (http://www.cruxis.com/chess/houdini.htm#Large_Pages):
In 64-bit Windows Vista/7 Houdini can benefit from so-called large memory pages.

So, no mention of XP...

But Large Pages with Windows XP Pro x64 work perfectly:
with Deep Rybka 4 x64
with the latest 64-bit IvanHoes (IvanHoe52fUS-beta, IvanHoe52gU(fix))

Does somebody here have Large Pages experience with Windows XP Pro x64 and Houdini?

Or maybe Robert can comment himself on why he left out 64-bit XP...

It is correct that Houdini will not try to activate Large Pages in Windows XP, for a simple reason: the Microsoft API documentation indicates that large page support requires Vista or higher. See the VirtualAlloc API call which states explicitly for the MEM_LARGE_PAGES flag: "Windows XP/2000: This flag is not supported." Also the GetLargePageMinimum API call has a "Minimum supported client: Windows Vista".

As apparently Large Page support does seem to work in XP 64-bit, I will take this into account for the next release.
Thank you for reporting this.