Login and registration form in a single page
This has been answered many times here.
See this Print registration and login forms on same page

For this You need to create a page for Registration like this 

page-user-register.tpl.php


And print the page contents as usual. 
in that page you could try render user_login_block

Additional resources 


http://www.trevorsimonton.com/blog/page-usertplphp-profile-php-template-drupal
http://api.drupal.org/api/drupal/modules%21user%21user.module/function/user_login_block/7