Use mint as the user name and hit enter. This may take you to the desktop, it does for me.
If not and you get a prompt for the password just hit enter as it should be an "open" password. At least that is what has been historically true.
A forum search for this problem would have gotten you that answer.
If it does not work you could reboot, modify the menu entry to boot to recovery (instruction string should simply ask for "single" instead of "quiet splash". Then boot up. Should get a tty log in. You can then play with the user name and password using mint for one, open for the other in various combinations and of coarse as both.
You may get a root prompt (#) anyway if that is the case just create a new user and give it a password, hit Ctrl + d should take you to a user prompt. Sign in as the new user.
Type "startx" and you should be in.
Dell XPS 420 Core2 Quad Q 6600, audigy5.1, Radeon HD 6450 - currently 4 320Gb HDD, Debian Squeeze for secure use, Debian testing for daily use, Debian Sid for fun.