wudup, may i suggest my mod that i am working on, if i can get it finalized with one bit of helpful coding that i just havent been able to think of here:
http://forum.x-cart.com/viewtopic.php?t=18857
check it out in action here, try the pumps category....
http://www.mindells.com/home.php
may not be exactly wut u are thinking of, but id like to help if i can...it would only load one subcat at a time, no java to have to preload for the flyouts, and much more search engine friendly.....