This is an interesting concept. I suppose the practical application would be to have a whole mess of scripts in a database online that anyone could play, without needing to download them?
I don't know anything about Java so I'm afraid I can't help you, though.
Not java, but javascript. Java requires a plugin, but javascript is the language built into the browser. Originally the idea was to just write a shooting game in javascript (there aren't many around yet), but I decided to make a danmakufu interpreter so there would be a set of scripts available to use.
That is an interesting idea though, I could have a web application where people could upload their scripts and people can play them, save replays, and easily share scores and such. That part would be easy though, the hard part would be writing the engine. That's a pretty neat idea.