yesssss. That was the second option I said. It doesn't have to be an oxygen tank. It can be any entity you want that's defined as a pickup. For script details you could search on health. I'm sure there are plenty of scripts on manipulating health. It's the same thing, just use whatever reserved word fpsc uses for oxygen.
As for the dead body, you can load the .x file of any character into any modeling app (ie Milkshape) and position it to a death pose. Now just use MagicFPS or whatever to make it a static entity to use in game.
Keep in mind I'm just guessing at a solution. I've not needed to do either of the things you're trying to do.
"I'm trying to find new ways to make this game more attractive." - Dennis Rodman