So what your saying is internet based multiplayer games are difficult to build?
Well they CAN be tricky to build, but I wasn't talking about that
I was saying it would be difficult to create an actual server (in the form of a Java app) because most webhosts don't let you run system commands (and like I said, their computers might not even have a JRE).
How about using mysql to hold the x y coordinates of the marbles on the gameboard? Can an applet write to a database? Then the clients could query the database to update their board.
This could be possible however it will use alot of bandwidth. Instead of the server telling the applets something has changed, the applet has to query the database over and over even if their is no change. What you might have in the database is a "modified date" variable for the applets to check. This way the applets would only query the board data when the "modified date" has change since the last modified date. Again the applets will be needing to check this quite often because the server can't notify the applets directly of any change.
I don't know how to get applets to query a database. I know there is a JDBC API you can use, however I'm 99% sure you need to sign your applet to use it. You will also need to find a JDBC driver to connect to a MySQL database. Try googling JDBC
If you can manage to have your applet query a database, then you can make a simple board game like this work. But unless you could run an actual custom server (as a java application), you won't be able to do things like MMORPGs because there's just too much data flying around (active chat, player movements, etc.).