WP can't select Database??? Newbie question.

I’ve been trying to set up WP and MAMP. I got through all the setup until the very last step. Then I got this error:
Can’t select database

We were able to connect to the database server (which means your username and password is okay) but not able to select the artsite_dp database.

Are you sure it exists?
Does the user root have permission to use the artsite_dp database?
On some systems the name of your database is prefixed with your username, so it would be like username_artsite_dp. Could that be the problem?

If you don’t know how to set up a database you should contact your host. If all else fails you may find help at the WordPress Support Forums.

Any ideas??
Thanks.