I was experimenting with the prototype.js library, thanks to all who have contributed towards this, and the wonderful documentations avaliable as download, as well as online references.
For a multilevel hierarchical selector of category, where the top levels should not be selectable, the existing ui elements were not enough to show off, with out incurring ambiguity. This led me to do the basic tests, and finalized the said widget. It does not support much now, though I may be working on a extension which will support multi-select.
See the Deep Category Select, in action where it is embedded into an example.