Not sure if this is right section, please move if it's wrong.
See the following:

<form action="{$config.base}{$config.dir}search.php" method="get">

  <input type="text" class="text" name="1" id="1" size="22"/>
  <input type="text" class="text" name="2" id="2" size="22"/>

    {assign var="1" value='input[id^=1]'}
    {assign var="2" value='input[id^=2]'}
    {assign var="whatwhere" value="$1""$2"} 

  <input:hidden class="text" name="what" id="what" size="22" 
  value="{$smarty.get.what|escape:"{$whatwhere}"}"/> 
  <input type="submit" value="{$lang.search}" class="button" />

</form>

Basically what I am trying to do in this form is take the field's, "1" & "2", values and combine them to be the value in the "what" hidden input.

Can someone tell me what I'm doing wrong and what to do to get it working.

Thanks
Dylan

Wrong

<input:hidden

Right:

<input type="hidden"

Or

<input style="display:none" ...