Ok, I'll admit, I'm not up on all the comic books. And I'm sure things are different in the Ultimate Spider-man Comics, but I'll stay out of there and with what I know, which is the TV show.
The original 3 parter was when they were bring back that sample from the moon I believe on the space shuttle. The symbiote was on some of the samples they were bring back and caused the shuttle to crash. Rhino went and stole the item, and Spiderman went to save the astronauts. The symbiote gets on his Spiderman outfit and eventually takes him as it's host. But the symbiote was trying to take him over completely, because as you watch, you see Peter getting cockier and angrier all the time. When he finally gets it off of him, it take Brock, who hates Spiderman as much as the symbiote does. And Vemon has all his powers as it copied them from Spiderman. That's what I got from it all anyway.
Now Spiderman, as we know, attached the symbiote to the shuttle and had it sent back into space. Mordo(sp?) Summons them back for the big fiery guy as it was about to reproduce. Vemon is back and Carnage is soon created through Cassidy. Vemon runs off after he completes his part of the deal, but Carnage stays around to help them get the life energy they need to open the portal to bring Mr. Fiery dude into our world. After a battle, the Fiery dude gets sent back, but has a link to Carnage, so they have to send him through. He trys to pull in this one Doctor that Brock likes, so he sacrifices himself to protect her and is sent into the portal as well.
And the humor in all of this? Yesterday morning and this morning on Jetex, they showed each part of the 2-parter with Carnage in it. ^_^
But I do agree (as you posted later) that the Actor playing Vemon is NO Eddie Brock.
Lurker Extraordinaire