Maybe your CD drive isn't reading it right. Have you tried if your copy of XP boots up from that drive?
First results of 3DMark are in, looks like 32-bit is faster in 32-bit 3D...
3DMark05, version 1.2.0:
WinXP x64, NVidia 6600GT AGP 128MB, stock settings (not OC'd), score: 2876
WinXP 32b, NVidia 6600GT AGP 128MB, stock settings (not OC'd), score: 2985
I might have to tweak the Windows settings on x64 side, the 32b is quite tweaked.