I was in your position last Month, I wanted to use my iPod in my car, I needed a new head unit, so I did some reaserach and found out that I had Three options.
One I could get a tape deck with a K7 (any one speak french?)
Two I could get a kenwood CD player and use a little box (40 extra bucks) and I would have a line in on the Cd changer thingy.
Or I could get a simple CD deck with a line in on the front.
I went to a perfessional guy and
#1 would cost me about 150 including installation
#2 would cost me about 190 including installation
#3 would cost me about 340 including installation
so I thought about it and went to some other places, Best Buy and Circit City, and I ended up getting a JVC CD deck with a line in on the front, for only 175 including installation not bad they also had Aiawas with line in but they suck ass.
So what am I saying, I would toss out the old tape deck get a CD deck with a line in. It bight be cheaper then you thought