fdisk -l smoothwall.img You must set cylinders.
You can do this from the extra functions menu.

Disk smoothwall.img: 0 MB, 0 bytes
16 heads, 63 sectors/track, 0 cylinders
Units = cylinders of 1008 * 512 = 516096 bytes

         Device Boot      Start         End      Blocks   Id  System
smoothwall.img1               1          11        5543+  83  Linux
smoothwall.img2              12          44       16632   82  Linux swap / Solar is
smoothwall.img3              45         240       98784   83  Linux
smoothwall.img4   *         241        1015      390600   83  Linux