Hi Mike,
Are you sure you mean the IPTC pad? (what height and width fields do you mean?)
Anyway, the IPTC pad is purely for the metadata and will not resize your image. If you want your image at a certain size, use Save As from the File menu, there you can specify height, width, minimum quality and max size (note: if you want to have your images not larger than a certain size, be sure to set a very low quality limit as the quality gets precedence over size!).
Hope this helps,
Hayo