Thats a toughie. See, Ford head units are usually manufactured by a company called JBL. I say that the J stands for Junk, cause thats mostly what they are. blablablah231 has a good answer yes. However, it should be noted that the FM transmitter does a lousy job with sound reproduced on the speakers.
The Cassette thing he's talking about is called a CD to Cassette Adapter. On the Fords that I've used those on, I found them a bit of a pain in the @$$ because it would goof up the head unit and make it go into "Seek" mode which is when the cassette player looks for another track on a cassette. Handy with an actual cassette, not one of those CD/Cassette thingies.
I would highly recommend getting your hands on a JC Whitney Catalog to price out new head units. Get speakers too while you're at it, you might as well.
There is many choices you have to connect your ipod to the car stero but it also depends on the ipod...
You can use a fm transmitter; basically finds a clear station with no noise and same station on ipod and then bam music goes through your radio heres a example of one but there are many ohers and cheaper too TuneBase™ FM with ClearScan
For car stereos with auxiliary line-in, you can connect the iPod to the stereo using "an extension cable with 3.5 mm stereo connectors on each end.
If you have a car stereo with a cassette player
, you can purchase a simple mini-plug to tape adapter that plugs into the iPod's headphone jack and the cassette deck.