You don't need BIOS remapping.
Check out:http://www.raymond.cc/blog/archives/200 ... gb-memory/
for patched kernels.
Basically, the address space of each process is still around 3GB (1GB taken up by I/O addresses). Windows will take up another 1GB, which means each process still gets around 2GB free RAM. But through PAE, all the physical RAM can be used if you have enough processes (VMs are good candidates).
I am running Windows 7 with a patched kernel, and using all 4GB of my physical RAM. Without the patched kernel, I only get to use 3.2GB physical RAM, which could make the difference between whether I can run 2 versus 3 1GB VMs.