Zootal and Jmac, Tomato seeds can be started indoors 6-8 weeks before
you expect to set them outside. I live in Philadelphia, and my last
expected frost date is May 15th. So I will add a week to that to be
safe making my outside planting date May 22nd. Lets jump backwards 6-8
weeks, and I will be starting my seeds between late March and early
April. Below is a link to a page that is all about starting tomato
seeds indoors. I hope it helps, and good luck in your garden!
http://sites.google.com/site/thetomatogardener/