it 'll be better to forget about http  protokol. I suppose that u need
a server  push mekanism. Why dont u use a tcp soket for this purpose.
By this way u can have a strong comminucation skills, without any more efford.
Serving a port  from an applet  will cause some security problems and also u need
to work with all client machines to correct these security exceptions.
write a soket server,allow your clients to connect this tcp server and make all
your
clients online. this will be more simple and easy. (offcourse if u havent got
clients more then 64K)