Sure, the ajax script is configured to make the scrollbar auto scroll to the latest/recent chat post. But you can play around with the css there, eg: to solve your issue you can customize the width property in the css file as your desire.
For example to your issue:
Find this line in the css file
#chats{margin:2px auto 3px 2px;[b]width:78%[/b];height:330px;border:1px solid #aaaafe;background-color:#fdfdfe;overflow:auto;padding:2px;box-shadow:.18em .18em .2em #a0a1d2;-webkit-box-shadow:.18em .18em .2em #a0a1d2;-moz-border-radius:.8em;-webkit-border-radius:.8em;-khtml-border-radius:.8em;border-radius:.8em}
In that line, you can edit the width css property into 100% to make it fit without scrolling. Else for the balance, the other optional is to set the width on #chatarea css tag into 100% too. So, your chat room will display fit to screen.
For other layout/display issue, all you can do is just to play arround with the css there.