This instructable basically sums up most of the login bypassing methods posted on Instructables.
Step 1: The golden disclaimer
Step 2: The easy part
If you have a login page like the one in the intro, go to step 2. If you have a login page like this one, it should be relatively easy to get into. Unless the default administrator account has been changed, all you have to do is type "Administrator" or "administrator" as the user name and the password will be either blank or "password". Then press "OK" and you should be in.