I didn't read any responses, but I'd recommend throwing the infant car seat away. They expire after 5 - 6 yrs (new ones actually have an expiration date on them). The plastic breaks down and it's not safe in the event of an accident. What I was told was to compare it to the plastics you leave out all summer and winter. It gets very brittle. I was told to cut the straps (so no one will stop and pick it up) and put it down for the trash collection. I know it seems a shame to throw these things away, but I've actually done it with a very expensive Britax car seat, as well as some other seats in otherwise great condition (a great infant carrier being one of them... but there were 9 yrs between the two kids and I heard about the expiration issue and was too nervous about using it). It kills you to know you are throwing away something worth several hundred dollars; but I think my child's life is worth it, and so is the child of anyone who would take the expired car seat. I don't know, maybe that is an over-reaction. Who knows how dangerous they really are after they expire.
That being said, there are others that think any car seat is better than none and they donate theirs. Yes, most womens' shelters take donations of baby items. I just couldn't do that in good conscience knowing that it might not be safe. A friend here called somewhere, I'm not sure where, and they told her to go ahead and sell hers at her yard sale. They used the 'An old seat is better than no seat' line on her. She did sell both of the seats in question at her yard sale.
I'd suggest calling the car seat safety experts in your area and asking them what to do with your set. They can give you facts to go on.
OK, done preaching. :) Have a great day!