Basic Setup Help Needed - Connecting an IP Address to a New Virtual Server

Hello,

I'm in the process of moving all of my big sites from a shared hosting plan to my own dedicated server. Because of its size, I want to give one site its own private IP that no other address.

My host provided me three IP's and I understand that I use the virtual server creation page to set the 'Network interface' option to 'Virtual with IP' and enter one of the IP's I've been given.

When I attempt to go through with this, however I get the error message: "Failed to create virtual server : The virtual interface IP address is already in use."

I'm not sure why it's giving me this error. Anyone have a suggestion for getting past this?

rob