I don't know specifically if the 1999 Windstar has a CD changer input, but you might be able to tell from the face plate of the stereo. If there are any buttons with markings for switching CDs, such as CD next or CD plus, then it probably has CD changer capability. In that case, you can get an adapter that will plug into the changer. Alternatively, you could replace the radio head unit with a new, iPod-capable head unit. These have gotten pretty cheap, so you wouldn't be spending that much more on it. We have an article on the best car stereos for iPod connectivity: http://reviews.cnet.com/4321-3425_7-6580784.html
Has anyone had their Windstar set up with a hard connection for and Ipod to the standard CD stereo? I think it has an input for a CD changer and I thought it might hook up that way.