Hi,
Have you had a look here?
http://help.x-cart.com/index.php?title=X-Cart:Special_Offers
I used this when it was a paid for module and had some good displays but that is quite a while back. I have been just modifying the price but I am going to start using this again for setting up in the future promotions that will run for 8 weeks each.
At present just put a simple one on but will be more involved when I get back into it.
June Highchair promotion available to 6:00pm 30th June 2013 10% off marked prices.
Discounted price will show when you click Add to Cart
It is on my home page and others, price only shows in cart but I'm sure it did used to show on the product.