I thought that might be right... then I saw this. The game status is on the right of the HUD (rounds, waves and sets) and the Spartan icon is on the left. It has something to do with Firefight Versus mode but I don't know how that works yet Edit: OK, in Versus mode the Spartans start with 5 lives. I think you'll get the achievement for completing the Versus game with all your lives remaining (so no deaths).
Update: Weird ostrich-like animals will be present on Reach. Looks like you get an achievement for killing them. So thats all Multiplayer and Campaign achievements found (unless you still have problems with the list). The remaining achievements are either "Player Experience" or "Training"
I think the Flaming Tank Achievment will be you have to protect a tank at some point in campaign.Just my opinion,But does anyone else think the same?
OK, the achievements are officially up on B.net I'll update the OP, most of them were right, a few were misplaced and some were wrong.