You're getting there with it.
1. You should ditch the table, and use <div style="float: right; padding: 3px;"> for the avatar placement
2. You shouldn't make a call to yet another CSS file from the headinclude, instead those definitions should be added to vbulletin.css since you're already requesting an edit there.
3. z-index: 2px; isn't valid. z-index can't have a pixel value and instead should be just 2 if thats what you want it.
4. Why not make use of the already built in vBulletin drop down menus, rather than adding another call to a javascript file.
Great work though!