If you want the username, you'll need to get it from the database. That either means making it a vBulletin page with vB function calls to get the username from the DB, or writing your own code to extract the info from the database. There are plenty of tutorials arround for making vB pages (at least, people are always linking to them...). As for the specifics, you'll need to call fetch_userinfo to get the user information:
Code:
$myinfo=fetch_userinfo(1);
Once you've done this, you can use $myinfo[username] to get the username of user 1. Where you put this depends on how you go about doing the vB page.