Intel centrino wireless-n 1000 support
can i use thin mini PCIe card as Wireless AP in PFsense appliance?
It may possibly be supported by the iwn(4) driver. See:
However it will not support any 'N' modes if it is supported at all. You would have to look into it more closely.
iwn driver doesn't support AP mode - see http://www.freebsd.org/cgi/man.cgi?query=iwn&apropos=0&sektion=0&manpath=FreeBSD+9.0-RELEASE&arch=default&format=html
For AP mode your best best is probably to use a card with an Atheros chipset.