Lynn,
I seriously doubt you would find a trustworthy source that specifically states that you need to allow an extra 2GB for PAE.
From what I understand, the amount of memory required to enable PAE is based on the size of the PFN database required to map the memory.
As previously stated, if the /3GB switch is enabled, the system will only map up to 16GB of extended memory due to the fact that the /3GB switch is limiting the kernel mode memory in the first 4GB of memory down to 1GB. Addressing more than 16GB of memory under /3GB would potentially cause the PFN database to consume too much kernel memory (but it depends)
If you are not using the /3GB switch, then the system will allocate 2GB of memory to the kernel mode system and 2GB to user mode applications (of the first 4GB) by default, so any calculations you make about how much memory to allocate to SQL server (for instance) only needs to allow for the 2GB of kernel mode memory and the requirements of other applications.
If you are allowing 4GB of RAM for the OS on a 32bit system, then that would cover the PAE requirements as the PFN database is stored in kernel mode memory, which is part of your 4GB allocation.
See this blog post by Mark Russinovich for some technical details, and maybe have a read of some of the other posts in the series. They are really informative.
http://blogs.technet.com/b/markrussinovich/archive/2008/07/21/3092070.aspx
MM
select geometry::STGeomFromWKB(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