T.
Here is some information that might be helpful...
http://www.ibike.org/education/infant.htm
http://hea-www.harvard.edu/~fine/opinions/childcarriers.html
I have a bike trailer for my 2 year old and really like it. I think it is more stable than a bike seat b/c it has a lower center of gravity. My son really enjoys riding in it. It is nice that you get some extra storage this way too if you need to carry along anything or pick a few items up at the store (my trailer has storage behind the seat).
Happy biking!