I like version 4.4's new popup box, so I wanted to make my own buttons (images - no text) which would popup a file in X-cart's box rather than a boring browser window.
Here's how:
1) The file you are popping must be a .php file, at least from my experience. I put mine in the site root (since user doesn't have permission to access php files in the static page area)
2) in /skin/common_files/customer/buttons/button.tpl:
Immediately before:
{elseif $style eq 'image'}
{if $type eq 'input'}
Add:
{elseif $style eq 'userbutton'}
{strip}
<a href="{$href|amp}" {if $onclick ne ''} onclick="{$onclick}; return false;"{/if} {if $target ne ''} target="{$target}"{/if}>
<img src="{$imgpath}" />
</a>
{/strip}
3) Then, in whatever template you want to add the button, insert something like:
{include file="customer/buttons/button.tpl" style="userbutton" imgpath="/skin/fashion_mosaic_grey/images/fashion_mosaic/freeship_icon.png" href="javascript
: return !popupOpen(xcart_web_dir + '/shipping_popup.php')"}
Here, I made a free shipping button (freeship_icon.png) which opens a php file (/shipping_popup.php) in X-Carts new popup box.
I'm sure this could be improved further - for example you could replace /skin/fashion_mosaic_grey with your skin directory smarty variable, but I don't know what it is off the top of my head. If anyone could improve this code or has suggestions, please post!
Works and tested for X-Cart version 4.4.1