How to know a server is running on a specified port?

From: Gordon (sdgwedh_at_hotmail.com)
Date: 12/25/03 

Date: Fri, 26 Dec 2003 00:56:56 +0800

Dear all,

How to know that whether a server is running on a specified port?

For example, server A is running on port 1888. For a client, how to know
this?

Thanks,
Gordon