Making a MUD from scratch Edit
A way to avoid having to show credits is to trash the current MUD you wrote based on Diku(or other codebase), and make a new one from scratch. In the start it is very painful to realize you have to throw away a lot of work, still it can be a very rewarding and exciting project. When making a MUD from scratch it is a good idea to try to make it different from current MUDs to try improve the state-of-the-art.
There's some literature that's nice to have access to:
MUD Game Programming is a book about making MUDs. It is a very good read to get started. Two MUDs are created: SimpleMUD, and BetterMUD. SimpleMUD is very simple with most things hard coded. The BetterMUD uses Python as scripting language to achieve greater flexibility and extensibility.
MUDDev Archive is also a very good resource. It used to be a mailinglist and is avaible as a read-only phpbb forum on the linked website. There are many interesting discussions there about developing MUDs, and is a good start to get ideas for a new MUD.
GameDev.net -- General Game Design has alot of articles about designing games. There's some articles about rpg design, and game balance which is very related to developing a MUD.
Designing Virtual Worlds by Richard Bartle is another read that's highly recommended.
There's also MUDs with less restrictive licenses like SocketMUD if one doesn't want to start entirely from scratch. For people who want a more built up base, but still don't want the licensing issue there's also NakedMUD which is completely in the public domain.