I'm not a moderator, but I'll try to help -
Before you can register for a new screen name, you have to logout from the existing one. You can logout by going to the link at the bottom of the 'home' page on the Disboards. To get to the 'home' page, click on the 'home' button at the top of one of the boards, but not from within a post.
Now some background info -
The Dis Boards keeps track of you by using 'cookies' that are stored on your computer, that's how it knows it is 'you' when you access them and if you want to be recognized without logging in each time.
If you create a new screen name for your husband, and you use the same computer, each of you will have to logout when you use the computer so that the next one can login. You will both have to change the options in your profile so that it does not keep you logged in. Otherwise, the last screen name that was using the computer on the Dis will be the name that is presented to the next person that uses it.
Also, you will need to use a separate email for each screen name.
All of it is manageable and will work well, it just takes a little getting used to so you can avoid a case of mistaken identity.
hope that helps