There's a better solution to this
first of all, have the html form in an include...
have the fields set up like this:
<input type="text" name="f_name" value="<? echo $f_name; ?>">
if there's an error, show the error, and include the form
since the variables that they filled out are already set ( they just subitted the form), then what they filled out will be there for them, without necessitating the use of the browser's back button.
If they're seeing the form for the first time, those variables have no value, so the fields will be empty.
-=Lazzerous=-