Java APIs

I've made a basic chat server/client using RMI. The clients register to the rmi registry as well in order to be 'callbacked' from the server whenever some client says something. It works fine but I have some questions.

is rmi appropriate for such an application or should I just use packets to send the data arround ? because I feel that starting 1 rmi service for the server and n rmi services for the n clients is a waste of memmory or cpu ? is that right ? would the system perform well if 500 clients were connected ?

in my windows 98 I start 3 clients in separate dos prompt windows and there is a noticable latency (lag) when the server calls the remote methods of each client. In my university server which runs solaris it worked very very fast. any thoughts ?

finally, how is it possible to start the 'rmiregistry' without having to tell people to run it manually ? is this possible ?

thanks