It is very easy to integrate Xcart with Nelichso. Please find here with the steps you can follow to integrate it.
1) Connect your zencart website through FTP.
2) Go to the folder includes/templates/template_default/common.
3) Download the file html_header.php.
4) Login to your nelichso account.
5) Click on menu " HTML Code " from left panel.
6) Select the type of code you want to use.
7) Paste it in html_header.php any where in
8) Uplod the file html_header.php to your website through FTP.
That is it. You are done.