Hi Pawan,
This is a typical problem that we face when building Client-Server based applications. There needs to be at least one static server which can help the client to resolve the end-server address. Typically in a WebServices scenario, this problem is handled by publishing your service to a central repository from where it is resolved by the client. If you are using RMI, you must be aware about the "Binding the server to RMI registry". The client "looks-up" for the server address in this registry and then invokes various operations on it.
With your issue, as far as my knowledge goes, you need to have the server as a static server. To overcome the DHCP assigning a different address to the server, you can make a DNS lookup for the "server name" to get its IP which can then be used by your client.
Regards,
Sanket Daru.