Verify those two input lines are inside a form. See if your form has a name. Verify you included the script blocks in home.tpl:
Code:
<script language=JavaScript1.3 src="{$SkinDir}/copybilling.js"></script>
<script language=JavaScript1.3 src="{$SkinDir}/copynames.js"></script>
Verify those js files exist in that location (i.e., /xcart/skin1/copynames.js). See if those script blocks show when viewing the page source while viewing the page that has the checkboxes.