I'm not familiar with Caldera, but I have used the FA-311 (with much headache involved).
First, the driver for the 311 should be named "natsemi.o", and the source-code file is "natsemi.c". The current source file can be obtained
here. Some NIC vendors will rename modules to reflect the name of the card (as it seems to be in your case), but compare your fa311.c to the natsemi.c I referenced above just to be sure. If they're the same, it should be OK.
If you have successfully compiled the fa311.o file, and placed it in /lib/modules/net, you can try to manually load/insert the module by doing "insmod fa311" or "modprobe fa311" (for modprobe, you might have to use fa311.o instead of just fa-311). After that, do "lsmod" to view all loaded modules. If insmod or modprobe worked, you should see the fa311 module in the list.
If this worked, add the line "alias eth0 fa311" to your /etc/modules.conf file to initialize the NIC/module at bootup.
Remember that UNIX is case-sensitive, so if your module is named, for example, FA311.o instead of fa311.o, substitute your exact filename for the filename I used.
Also- if you do the above, and everything seems to go OK, but on reboot the NIC fails to initialize, try turning off Plug-N-Play support in your BIOS; it can cause conflicts with some cards under Linux.