[TelaFirma]

...edited to reflect changes made later on in this post...

Here is a mod that will hide the submit button until they check the box that they agree.

Step 1
Create the file /skin1/hide_block_script.tpl with this contents:

{literal}
<SCRIPT type="text/javascript" language="JavaScript 1.2">
// Function to flip visibility of certain div objects
function flipdiv(el,state) {
   if(state=="show"){
      status="block";
   }else{
      status="none";
   }
   document.getElementById(el).style.display = status;
}
</SCRIPT>
{/literal}

Step 2
Open the file /skin1/customer/main/checkout.tpl for editing.
At top of the file right before the first {capture} insert the line

{include file="hide_block_script.tpl"}

Next look for the line:

{$lng.txt_you_are_agree} "{$lng.lbl_terms_n_conditions}" {$lng.lbl_and} "{$lng.lbl_privacy_statement}".

and add this right after it:

No<input type="radio" name="agree" checked="checked" onclick="flipdiv('checkoutbutton','hide')" /> Yes<input type="radio" name="agree" onclick="flipdiv('checkoutbutton','show')">I Agree to the Terms and Conditions

Next find the section that looks like:

{include file="buttons/button.tpl" button_title=$lng.lbl_submit_order style="button" href=$button_href}
{else}
{include file="submit_wo_js.tpl" value=$lng.lbl_submit_order}
{/if}

and change it to read:

<div align="center">
<table border=0 cellpadding="0" cellspacing="0" id="checkoutbutton" style="display: none;">
<tr><td>
{include file="buttons/button.tpl" button_title=$lng.lbl_submit_order style="button" href=$button_href}
{else}
{include file="submit_wo_js.tpl" value=$lng.lbl_submit_order}
{/if}
</td></tr>
</table>
</div>