To enable support > 3.25 GB RAM in Windows XP SP3, patched kernel is needed.
Three sets of patches are on Internet.
It contains:
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP 64G" /kernel=ntkl64g.exe /hal=hal64g.dll /fastdetect /PAE /noexecute=optin