You are a bit sparse in your explanation of the problem. Exact commands and error responses are always preferred. But since you mention ath0, I will make the assumption that you are using madwifi-ng drivers.
If this is the case: You need to remove any VAP's (athX) and change the MAC of wifi0, then create a new VAP using wlanconfig, adding the -uniquebssid option at the end. (you can search the forums here for a more detailed explanation).
To make this permanent, put the commands into the rc.local file or something similar. If you don't know what rc.local does, google that as well.
Now, with this new found info, google away and have a great time learning more about linux.


Thanks

