Using $_GET for POST

>
if ( ! (isset($_GET['xxxxx']) && $_GET['xxxxx'] == 20) )
{
// Do something by returning an error
}
>
Can this ever be correct when the form looks like:
>
<form ENCTYPE="multipart/form-data" ACTIN="" METHD="PST">
<input NAME="SomeFile" TYPE="file">
<input VALUE="submit" TYPE="submit"></form>
>
?


I sometimes do things similar to this. I normally use it when I am opening
a new page via a javascript function and want to pass several values to use
or check in the new page.