In order to use Shopp, you need to have cURL installed and running as mentioned on the features page. Use this plugin to determine whether your WordPress setup has everything you need.
However, XAMPP does not come with cURL already ready to go. In order to make your local WordPress installation compatible with Shopp, you need to turn on cURL.
First, locate your php.ini file in your xampp folder. If you went with the generic login, then the php.ini file can be located at C:xamppphpphp.ini.
Then, it’s really quite simple - uncomment extension=php_curl.dll in your php.ini file, then restart Apache.
Once you have done this, save. Stop Apache, refresh and restart Apache. Everything you need to run CURL on a XAMPP install is included in the download.