I can't see either of you getting much help unless you provide hardware specs (CPU, motherboard, network card), dmesg output (of the network adapter being detected), what version of FreeNAS you are using (8.0.1-RELEASE? i386 or AMD/x64?) etc.
Have you checked the FreeBSD message boards? FreeNAS is based on FreeBSD 8.2, so if FreeBSD 8.2 doesn't support your hardware there's not much chance of FreeNAS doing so.