Today I saw a post on the DotNetNuke Forums about setting up a different display name to appear when the user posts. Specifically they wanted to be able to display the First and Last Name of the author with each post. The solution was for the person to modify the DotNetNuke Forum source code.
Now, the DotNetNuke Forum Project does give each forum user the ability to specify an alias, but this is optional and the administrator has no way of controlling how it is used.
Active Forums makes it very easy for you change the name that appears with each post. Active Forums has a
Display Name setting that has four options: User Name (default), First Name, Last Name or Full Name.

You can change this option at any time and it will immediately be effective for all your new and existing posts.