redirects to main page after login:
<a href="http://yourdomain.com/wp-login.php?redirect_to=http%3A%2F%2Fyourdomain.com?height=475&width=600&modal=true" class="thickbox">Login</a>
redirects to dashboard after login:
<a href="http://yourdomain.com/wp-login.php?height=475&width=600&modal=true" class="thickbox">Login</a>
