I see.
Make sure you fix the classes in stylesheet (style.css), for instance the default width of input fields for shoutbox is set to 130px
.shoutinput {
background-color: #FFFFFF;
font-family: Tahoma,Verdana,Arial,Helvetica,sans-serif;
color: #0f5475;
font-size: 11px;
WIDTH: 130px;
}
The textarea style doesn't have any width, so default is used, perhaps try set it manually in stylesheet as well.