Legal talk: IP and the idea/expression divide in US law

I am here talking about this: http://en.wikipedia.org/wiki/Idea–expression_divide

For some things, it’s easy to see which side of the divide it is but what I want to know is where the line lies. I am having difficulty determining what the legal criterion is and am more familiar with Canadian IP law and US IP law.
To take a concrete case, the idea of power armor is now rather widespread in sci-fi settings. It is used in StarCraft, Warhammer 40K and Fallout. It seems to be derived from Heinlein’s 1959 book Starship troopers.

The entity of “power armor” seems to be an idea rather than an expression. What would it take for the IP holders of StarCraft, Warhammer 40K or Fallout to be able to sue if someone used power armor in their movie/game? Would it require that the models of power armor be so similar that they’re difficult to tell apart?
To take another concrete case, how close could someone get to making a James Bond clone without infringing on someone’s IP?

(Note to mods: I am here looking for a staid discussion of the law, not arguing about whether it’s good or bad and not looking for advice either. This is why I suggest that GQ is the best section for this thread)

Not a lawyer, but a copying a specific image or a verbatim description would be copyright infringement. Anything less would be fair use or not infringement at all.

In general, copyright infringement only applies to exact copying; anything less is allowed. The only exception is when a a work copies the themes of a work pretty blatantly.

For example, I rewrite every sentence of Heinlein’s Starship Troopers and change the names, but the plot, themes, and sotry are utterly the same. That might be copyright infringement, but it would depend on mine (and Heinlein’s) lawyers.

(Take this with a grain of salt, I’m just a guy who reads things online.

Copyright infringement is making copies of a work without permission. A James Bond clone is perfectly acceptable (look up the Matt Helm movies, for instance) as long as you’re not just taking a James Bond novel and changing the names.

The issue is usually trademark infringement. James Bond, as it happens, is trademarked, so you cannot publish a book about his adventures – even if they’re completely original – without permission from the trademark owner.

But you can easily write an original novel about a UK master spy that looks just like a James Bond novel, as long as you don’t reference Bond or any trademarked catchphrases.

“Power Armor” would have to be trademarked (and it doesn’t seem to be), and the trademark could only apply is certain specific usages (e.g., video games). Assuming the trademark is allowed , it would have no application to an author. The first amendment trumps copyright law; the trademark holder will be reduced to writing a letter telling you it would be nice if you stopped using their trademark incorrectly.

But they will save the lawsuit for a serious threat to them – there no reason to risk losing a trademark over a use in a book. Also, by writing the letter, they’ve defended their trademark, so they won’t lose it if a real case occurs.

In video games, I often see weapons named “KA-57” when it evidently looks like an AK-47 or RA17 when it looks like an AR15. Are you saying that the game developers could squarely call them by their proper, trademarked names and it’d be fine?

Car racing games also seem to have trouble with trademarks. Car makers seem hesitant to have their car models damaged in-game. Could developers really include car models that look like a Ferrari or Lamborghini, call them as such and bang them up as much as they want and not have to worry?