This is the easiest way to do it. Just copy one of the existing dropdown codes. Just incase you didn't know what to copy, copy this:
Code:
<tr><td class="vbmenu_option"><a href="member.php?u=1">My Profile</a></td></tr>
And place it below all of them, or wherever you want your new dropdown option to appear on the list.
Now, first thing to do is change the a href URL (where member.php?u=1 is), change it to wherever you want to point it. If it's to another vB page, keep it in the same style it has here. (For example, just leaving the name of the file, nothing else, like it does with member.php in this example)
Next, change what you want it called. So change "My Profile" to whatever you want the link to be named.
Save. That should be it.