Hi Mike,
To clarify, the FatFreeCart code we provide at FatFreeCart.com doesn't have a download feature like our E-junkie (or FatFreeCartPro) service -- but the cart should look pretty much the same. An E-junkie cart can still display within your blog without opening in a new window.
To do this, be sure that you have a View Cart button on the same page as your Add to Cart buttons and that you are using the default Javascript-enabled versions of our cart buttons.
If you are already doing this and your cart is still opening in a new window please send us an email with your sales page and we'll be happy to take a look at the code. 
