This may help:
http://wiki.jqueryui.com/w/page/12138128/Tree[
^]
The source code for the tree is available, so it should give you some idea about how to achieve this.
A horizontal tree with a 100 child nodes, seems like an odd idea. When you expend the node things are probably bound to get cumbersome from a user perspective. If this turns out well I'd really liked to get a look at it.
Update:
Kasson found you a good link, exactly how this will turn out with a 100 child nodes will be interesting.
Regards
Espen Harlinn