[Skyrider]

That would require a template edit.

Template: header

Find:

PHP Code:

<vb:if condition="$show['registerbutton']">
                <li><a href="register.php{vb:raw session.sessionurl_q}" rel="nofollow">{vb:rawphrase register}</a></li>
                </vb:if> 


Change it to:

PHP Code:

<!-- <vb:if condition="$show['registerbutton']">
                <li><a href="register.php{vb:raw session.sessionurl_q}" rel="nofollow">{vb:rawphrase register}</a></li>
                </vb:if> --> 


The <!-- and --> around the code makes it so that the code will be ignored. I wouldn't suggest in removing it, just in case you might wish to re-add it later on. If that is the case in the future, just remove the <!-- in the beginning and --> at the end.