Need offer box to pop up before customer checks out

What is it called and how do I make a box appear when a customer is checking out that says something like "add two books to your order for only $5.00"?

Is that upselling or cross selling?

I need to move some inventory and want people to throw these items into their cart before they complete the checkout process.

HELP please.
raelynn

check out the cart upsell in the free downloads section. It's specifically for the shopping cart page. But, the way it is, it's not a popup, but you can move the code block so it appears above the cart contents so it's highly visible. I think you might need to add the cross sell for it to work, but I would recommend using the cross sell - actually I recommend the just another corss sell mod - anyway to help "biggie size" your orders.

There is a free download for an upsell / cross-sell mod for the shopping-cart page.

Can some one explain to me exactly how it will appear when installed on my site? I'd love to see an example of a website that used this download so that I understand its function.

thanks
rae