Many, if not most, IDX providers offer map search functions. If yours does, all you need to do is create a picture of the map search page and attach it to your homepage. Then assign it a link, so that if someone clicks on it, they get re-routed to the actual search page. See below for my company's Seattle-based website as an example.
Actually, it looks like we've updated it to embed the map into the site, itself. If your IDX provider can do that for you, then great. If not, the picture with link attached is effective and simple. - Wed Oct 20, 2010