32 Bit Performance on 64 Bit Windows

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Well, it is always hard to convince people that 32 bit processes are running on 64 bit Windows as first class citizens just like those 64 bit ones. So if you still have doubt, launch a web browser and navigate to this KB article. Hope these words help,

You may not experience decreased performance when you run a 32-bit program on the x64-based versions of Windows Server 2003 and of Windows XP Professional x64 Edition.

Well, Wikipedia also provides a similar description based on hardware,

Since the basic instruction set is the same, there is almost no performance penalty for executing x86 code. This is unlike Intel's IA-64, where differences in the underlying ISA means that running 32-bit code must be done either in emulation of x86, or with a dedicated x86 core, making the process extremely slow and essentially useless for backwards compatibility. However, on AMD64, 32-bit x86 applications may still benefit from a 64-bit recompile, due to the additional registers in 64-bit code, which a high-level compiler can use for optimization.