This can be done by adding in the extra string that will tell Joomla to take you to the login page.
In Joomla 1.5, add this string to the end of the website's domain in the URL address bar of your browser.
This will automatically take you to the login page of the Joomla website allowing you to login to the front end.
For Joomla 1.6 and above just use
The default view for the com_user is set to the login screen so that is the only part of the string that you'll need.
Login via the form that will appear. It is as easy as that.