There are several ways to get what you want..
You can add <img src="{$ImagesDir}/spacer.gif" width="150" height="1" alt="" /> before the "back" code. That will put a 150 pixel space between your buttons.
You can make the table cell that the "back" code resides in align to the right... <td align="right">.
You can add a "AlignRight" class to skin1.css and make the cell align that way... <td class="AlignRight"> (add .AlignRight {align: right; } to skin1.css )