Reverse DNS lookup

We are trying to setup a reverse dns lookup on our server.

We have a Novell Domain Name Server on a Windows Server 2003 OS with Novel Client 4.91 w Sp3.

We also have Pix 520 firewall which could be blocking it as well.

We are not sure whether we setup the reverse lookup correctly or how we would tell if the firewall is blocking it.

Help!

Thanks.

Shanon