I actually just went through this process myself. First, run the "dir flash:" command to see if you have anything in flash (this may require the "flash_init" command first). If you have an IOS copy, it may be corrupt and you should delete it before proceeding. If not, proceed away!
Next, run the "ether_init" and "tftp_init" commands. This turns on the Ethernet interface and enables TFTP. You'll next want to use the "set" command to change the IP address. You can change it to anything, really, as long as it can access a TFTP server on your network, or maybe access your PC directly via a cross-over cable.
Next, run the "tar tftp://TFTP_SERVER/FILENAME" command (I think this is right, but you might need to play with the syntax a bit). This will unzip the IOS file directly to flash. This is usually required because the 1200 doesn't have enough flash to store the tar file and unzip it at the same time.
I hope this helps! Let me know if I forgot anything, or if this doesn't work for any reason.