This is the basic login form, the same HTML code is used wherever this form appears, normally at the top of the #secondary content <div> (a .sidebar). The only times this is not the case are when the user is already logged in or when the user goes to the 'My Account' page (or any of its subpages). In the latter situation the login form appears in the main body area - #primary.
One thing to note here is that when the form is in the sidebar area the <legend> is replaced by a <h3>. This is to enable easier and more flexible styling of forms in the .sidebars.
<form action="/" method="post"> <fieldset> <legend>Sign in here.</legend> <ol> <li class="text"><label for="usr">Username:</label> <input type="text" id="usr" name="username" size="16" /></li> <li class="text"><label for="pwd">Password:</label> <input type="password" id="pwd" name="password" size="16" /></li> <li class="checkbox"><label for="rmbr">Remember me?</label> <input type="checkbox" id="rmbr" name="remember" value="1" /></li> </ol> </fieldset> <fieldset class="submit"> <input type="submit" class="submit" id="go-login" value="Login" /> <input type="hidden" name="action" value="login" /> </fieldset> </form> <ul> <li class="forgot-link"><a href="/forgot.html">Forgotten your password?</a></li> <li class="register-link"><a href="/register.html">Register</a></li> </ul>