Custom Wordpress Search

I need a simple "search auto completion" function integration into wordpress. The custom search is for a coupon site. Basically, you type in letter 'a' it will list all the stores starting with 'a' and narrows it down. If it does not have the store or word you are searching for, the box disappears and the regular wordpress search function is used. It should be based on --> [login to view URL] What I need: - I need to determine the "store" (example Aragos, AA Car Insurance etc) and set a custom link - If the customer clicks on the store, it brings him to the post/ page I determined before. -If there is no store match, it will use the regular wordpress search function An live example would be: [login to view URL] or [login to view URL] (look at the search field). Note: this are not my sites, it just has the same functionality I need and it based on the same code. I will send you the wordpress theme.