[totaltec]

Here are a couple options:
http://www.x-cart.com/extensions/modules/cloudsearch.html

http://www.thexcartstore.com/predictive-search-module-xcart.html

http://marketplace.x-cart.com/addons-modules/product-navigation/product-search/

Hope that helps! One thing to make sure of, is that your server and DB can handle something like this. It can be a resource hog.