I am somewhat knew to php.
I am asuming you are using <form method="post" ...
I think you could just do something like this:
echo "<form><input type=\"text\" name=\"tboxName\" value=\"".HTTP_POST_VARS['tboxName']."\"><form>";
when you create your forms. Doing this you would loose any default values you wanted to set up so you could set up your variables early on like this:
if ( !HTTP_POST_VARS['tboxNAME'] )
$tboxName = 'some value';
I hope this works for you.