I have limited knowledge myself, but as far as I know most stereos have standard connections. When you take the Ford stereo out you'll find three plugs on the back (power, speakers, aerial). If these won't fit directly to your new stereo then you'll be able to buy a simple converter for around £10 from Halfords/anywhere similar (you may need a separate converter for the aerial).
Assuming you want to fit a standard sized stereo, you also have the problem of the big gap left by the Ford stereo. For this you can buy a surround that will fit around your new stereo and neatly into the gap, for less than a tenner I think.
Nick, January 2005