To get round the error on Windows where the word list can't be found inside functions, take the call to pspell_new() out of the function and pass the return value to your function, i.e.

<?
function testSpell($pspell_link) {
    echo pspell_check($pspell_link, "test") ? 'OK' : 'Not OK';
}
$pspell_link = pspell_new("en");
testSpell($pspell_link);
?>