Don't use a plugin
The plugin author is probably missing the soundmanager2-nodebug-jsmin.js file if he's using the lights from that version.
Download this zip, upload the 2 files in it to your MYBB_ROOT/jscripts folder. Then modify your headerinclude template, and add:
<script type="text/javascript" src="jscripts/soundmanager2-nodebug-jsmin.js"></script>
<script type="text/javascript" src="http://yui.yahooapis.com/combo?2.6.0/build/yahoo-dom-event/yahoo-dom-event.js&2.6.0/build/animation/animation-min.js"></script>
<script type="text/javascript" src="jscripts/christmaslights.js"></script>
You'll also need to place
http://www.schillmania.com/projects/snow...64-top.png in your MYBB_ROOT/images
NOTE: I've already modified the scripts to work with the images being in images/ instead of image/ like he has.
I take no responsibility if this doesn't work perfectly for you
Its your job as a web admin to make sure things work, and this is totally untested.