For the sake of an easier explanation, I will ask my question through an example:
Say I have a Terra Stomper (8/8, Trample) and I attach a Basilisk Collar (Deathtouch/Lifelink).
I attack with Terra Stomper now... Terra Stomper is blocked by another 8/8 creature. Does all the damage clear and kill both creatures off, or can I say "The Terra Stomper deals 1 damage, kills your creature, and then 7 more damage directly to player/other blockers via trample?
Essentially, in the case of a trample deathtouch creature attacking, what happens when it is blocked by something with more than 1 toughness?