refresh for php/mysql chat

Hi, I wrote a chat using php/mysql.. and everything is working fine, except that I despise the meta auto-refresh - its really irritating :-) So I was wondering if anyone of you are aware of an alternative - if you do, please do help me out. Also, to show the users online, I simply do a "select" retrieve from the users table, and I delete an entry if the user logs out. But what if the user does not log out and simply closes the window - what have you done / or would do to delete the entry from the table? Is there a way to check all the cookies (I'm using cookie for login) and see if there is a certain value of the cookie that does not exist? If I could do that, then I could delete the entry... Thanks, sarahana