Checkout this page here, which shows a pretty radio button bouncing about a box, powered by JavaScript (albeit rather poorly hackishly programmed JavaScript):

http://www.avid-insight.co.uk/sl/bouncing-ball3.html

Now, download and run SL client version 1.19.1 (it may need to be Release Candidate), and on your own parcel of land, set your media URL to the above address. Setup an appropriate media prim, and hit "play". :)

(For those of you without your own land, we'll be setting up demos of this stuff soon in the 'Sloodleville' area of the "virtuALBA" sim. Do come along!)

It's fairly slow, and as yet SL doesn't allow interaction... but it works! It manages to update itself about 4 times per second by the looks of it, which is more than enough for most (sensible) purposes.

Rock on Linden!