some help needed building chat-app

i'm working on a chat-app which has to be extremely plain and simple mysql is available i tried stripping some of the big scripts, but ended up in a mess so i've ended up building a little app myself i'm just wondering whether i'm using the right principe to get the data refreshed in the chat.. i'm dropping all the messages as records in a mysql-table then i have the php script first printing all the html>>> stuff opening a paragraph and then a loop, querying the mysql, printing the data and querying again is that a way to build this, or are there much better ways? and some other questions: * how can i make sure the db-connection is closed before the user closes the window? * is there any server-side problem with this (say, 100 people log on, and are contineously querying mysql, won't there be some sort of crash?) thanx a lot michiel