Use the php_pspell.dll that is included with your version of XAMPP, it should be in \xampp\php\ext.
You kinda omitted/stepped around the XAMPP version you have installed. 1.7.1?The binaries have to be VC6 binaries, compiled for the exact version of PHP/Apache you have installed.
-- Because XAMPP for Windows' PHP is compiled as an Apache Module.
You can search the forum on 'compile', 'VC6' or 'VC9' for the details or read this:http://windows.php.net/download