Cool -- here's an example:
Let's say your Linode has an IP address of 10.0.0.44, and you've registered "example.com" and have DNS serving it up somewhere.
You want "mylinode.example.com" to be the reverse for your IP.
First you've got to make mylinode.example.com resolve to 10.0.0.44 in your DNS server...
Then, go into the RDNS manager, lookup "mylinode.example.com" and it will perform a forward lookup. It finds that the hostname resolves to one of your IP addresses, and then asks you if you want to use it as the reverse for 10.0.0.44. You answer "Yes".
Done
Make sense?
I need to put instructions on that page
-Chris