Depends on which version you're running. For 1.2, see the FreeBSD 4.11 hardware compatibility list. For the latest 1.3, the FreeBSD 6.3 hardware compatibility list.
If you're trying 1.2 and your cards don't work, I'd suggest skipping the HCL and trying 1.3. If that doesn't work either, then it's time to check the HCL and the "no interfaces detected" section of the handbook.
http://doc.m0n0.ch/handbook/