I've redone the checkout process for both 3.5.x and 4.0.x versions of x-cart and provided it as a module for just $99.00.
You can view details here:
http://www.websitecm.com/store/customer/product.php?productid=69&cat=0&page=
It:
Works with your existing layout to use your custom look and feel.
Uses the language database for multilingual sites.
Easily integrates into heavily modded x-carts.
Works with both 4.0.x and 3.5.x versions of x-cart.
Outlines the checkout process with straight forward steps indicated with tabs across the top of the checkout process.
Streamlines the checkout process removing long, messy, and confusing pages.
Removes potential distractions during the checkout process by placing the checkout outside of the store layout.
Allows for a user login or a user registration on the same page, avoiding any confusion for visitors.
Upon login, it moves the user forward in the checkout process, instead of back a step to the cart like the default x-cart.
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