I assume you are running Linux. SSH to the server and log in. Type:
It should tell you if that IP is up. If you do not see your other IP listed then your IP isn't set up.
If it isn't listed just type:
ifconfig eh0:1 <IP address> UP
It could be some sort of DNS slipup as well. I won't get into how the records should be created here, but just type:
service named restart
service httpd restart
The first restarts the DNS server assuming you do run one yourself and the second restarts Apache.