I've installed the game and started a new world with C3/DS and it is asking me now to login or register but when I click the link tor egister it takes me to http://www.creatures.net/ which doesn't give me a way to register.

How can I get past the login screen?

Registration for Docking Station has been closed down for years, unfortunately. What you need is the DS Offline Option, which bypasses the forced login so you can enjoy C3/DS offline. First, though, have you installed the Remastered Patch? It's necessary for the GOG.com installations so that third-party additions will work properly and be available to use in the game. Have a look at a few of the other topics here on the forum, which have a few other recommendations. Good luck, and I hope you can get it working very soon!