We used to have an article here about styling textareas with CSS in IE. It was one more post on the web about one more bug in Internet Explorer 6. It has been fixed in between.
In case you still need this, we had a workaround which consisted of applying width:100% on a div around the form, like this:
<div style="width:100%"> <form> <label for="t1">Try to type in here:</label> <textarea id="t1" style="width:100%">Try to type here!</textarea> </form> </div>