Whether the memory manager in the Windows kernel uses PAE is configurable through the pae boot option. Indeed, 32-bit Windows Vista is supplied with two kernels:
an ordinary kernel which uses 32-bit PTEs without PAE, and has no code for working with physical addresses above 4GB;
a PAE kernel which uses 64-bit PTEs with PAE, and does have code for working with physical addresses above 4GB.
The two kernels are respectively NTOSKRNL.EXE and NTKRNLPA.EXE, both in the Windows System directory. The loader (WINLOAD.EXE) knows how to set up the linear address space for mapping to physical addresses with or without PAE, but each kernel is specialised to one algorithm for the mapping. The pae option tells the loader which kernel to load.