I have the same problem. But i know any thing more.
I have to instalation of i386 arch with good work of wifi Intel (R) PRO/Wireless 3945AGB.
But when i install i386 with PAE put the same error that amd64 arch.
wpi0: fatal firmware error
I think is the NX bit.
Because the amd64 arch is activate and when you compile the kernel
i386 with PAE and you have 4GB or more of RAM, you have activate the NX
I have a dell XPS 1530 and have a cpu with XD.