Theming of User page
Customizing and Overriding User Login page, Register, and Password Reset in Drupal 6 and 7

Customizing the user login, register, and password reset pages is fairly simple, and uses the following concepts:

preprocessing to set variables
registration of functions in the theme registry
creation of one or more theme templates.


Step 1.
In the site theme directory, create or edit your template.php file.

Step 2.
The first step is to implement hook_theme for your theme. In the template.php file for your theme, look for a function named yourtheme_theme() and modify it to add these return values. If the function doesn't exist, add the following:

For D6:

&lt;?php
/**
 * Registers overrides for various functions.
 *
 * In this case, overrides three user functions
 */
function yourtheme_theme() {
  return array(
    'user_login' =&gt; array(
      'template' =&gt; 'user-login',
      'arguments' =&gt; array('form' =&gt; NULL),
    ),
    'user_register' =&gt; array(
      'template' =&gt; 'user-register',
      'arguments' =&gt; array('form' =&gt; NULL),
    ),
    'user_pass' =&gt; array(
      'template' =&gt; 'user-pass',
      'arguments' =&gt; array('form' =&gt; NULL),
    ),
  );
}
?&gt;


Notes about that code:

Change the function name by replacing "yourtheme" with the name of your theme
The template can be the same for all three. The example above uses a different template for each case: user-login, user-register, and user-pass
The template names must use a dash, not an underscore
Note: It's user_pass not user_password


For D7:

&lt;?php
function yourtheme_theme() {
  $items = array();

  $items['user_login'] = array(
    'render element' =&gt; 'form',
    'path' =&gt; drupal_get_path('theme', 'yourtheme') . '/templates',
    'template' =&gt; 'user-login',
    'preprocess functions' =&gt; array(
       'yourtheme_preprocess_user_login'
    ),
  );
  $items['user_register_form'] = array(
    'render element' =&gt; 'form',
    'path' =&gt; drupal_get_path('theme', 'yourtheme') . '/templates',
    'template' =&gt; 'user-register-form',
    'preprocess functions' =&gt; array(
      'yourtheme_preprocess_user_register_form'
    ),
  );
  $items['user_pass'] = array(
    'render element' =&gt; 'form',
    'path' =&gt; drupal_get_path('theme', 'yourtheme') . '/templates',
    'template' =&gt; 'user-pass',
    'preprocess functions' =&gt; array(
      'yourtheme_preprocess_user_pass'
    ),
  );
  return $items;
}
?&gt;


Notes about the D7 version:

The 'path' lines tell Drupal where to find the .tpl.php files. This is optional, and in the code above, 'path' tells Drupal to find the files in the templates subdirectory of the theme's base directory.
Note the "_form" added to the user_register element.
Note: As it is the case for D6, it's user_pass not user_password


Step 3.
Now you implement three preprocess functions. There may be more concise ways to code this, but this works very well and is easy to read, so here we go!

For D6:



Notes about that code:

Change the function name by replacing "yourtheme" with the name of your theme
The line $variables['intro_text'] adds the text that follows to the $variables array, which gets passed to the template as $intro_text
The second line renders the form and adds that code to the $variables array, which gets passed to the template as $rendered


For D7:
The code is even simpler for D7 because we don't need to pass a variable containing the form content we want rendered. The variable exists already in the $vars array and can be rendered in the .tpl.php file.



The above preprocess functions simply add a variable into the $vars array that is then displayed in the .tpl.php file. Much more complex manipulation of the content of the render array is possible.

Please note, that the preprocess functions should go into the template.php file.

Step 4.
Create template files to match the 'template' values defined above.

For D6
We need the following template files (make sure to use a dash, not an underscore) :

user-login.tpl.php
user-register.tpl.php
user-pass.tpl.php


For D7
Same as D6, except using user-register-form.tpl.php instead of user-register.tpl.phpfor the register form.

Step 5.
Paste the following into user-login.tpl.php. Modify as necessary for user-register.tpl.php (D6) and user-register-form.tpl.php (D7):

For D6:




  


For D7:




  


Note the change to the syntax for causing Drupal to render the form. Also, the D7 sample uses a different class for the div, but that's just a matter of preference.

Step 6.
Save your template.php file to the theme's main directory. Save your .tpl.php files in the same place for the D6 examples, or, in the case of the D7 examples, to the directory you specify in the 'path' element of the $items array.

Step 7.
Rebuild the cache. Go to Administration > Performance and click on "Rebuild Cache" on the bottom of the page.

Now, the user login page will contain the new text from the preprocess function, and the tpl.php file(s) can be modified to suit the site's needs.

reference : Customizing and Overriding User Login page, Register, and Password Reset in Drupal 6 and 7