[Lynne]

So you want it to fill the area? It's a textarea box and so you need to set the width in the code. This is from the source code. It's 60 cols wide. If you want it wider, you need to change that:
<textarea name="message" id="vB_Editor_QR_textarea" rows="10" cols="60" style="width:100%;height:100px"

This is what is in the area for when you hit Post Reply:
<textarea name="message" id="vB_Editor_001_textarea" rows="10" cols="60" style="display:block; width:540px; height:250px"