I'm sure source code will be kicking around somewhere. As for downloading Java for Windows (and thus IE) you can get it from Sun or the M$ site, but it isn't small unfortunately -- it's about 10Mb (or the Sun installer is anyway).
It does time people out after a time, sbdi. (I only know this cos someone got timed out while I was there!)
The same thing would be more than possible with PHP. Have a look at this. A PHP3/Flash 4 solution. (The second link when banging 'flash PHP chat' into Google.) I have no idea what it's like as I have never even looked at it, but it has a decent rating.