I came across this problem too.
I didn't want to use a java chat routine (though they aren't difficult to set up), but wanted to use an asp chat, however as gary suggests you would need to refresh the page often.
My solution was to only upload new lines of chat from the client to the server. I then updated the client by storing all the chat data in an xml file and reloaded the xml file using javascript and xsl.
Just an idea.