is the only Dog board I know of that we have guest. Did you get your password sent to you? If you think you might have made a mistake in your email address email email@example.com with the username you chose, and the email you meant to use with it-if you did NOT get a email with your password then you can't log in. If you have cookies enabled and have received you r password a common mistake is havint a 1 when it wants a i or 0 when its a o, so make sure you copy it correctly and in put it into the Log In box that will pop up when you hit the 'Log In' link to the right of the Register link.
If the above doesn't help, like BbBrdigeaddict suggested, go read that topic on log in troubles-see if your browser passes the cookie test and see if you can't get logged in using the tips in that thread.