For a D&D hack, there needs to be a good, flexible Nature theme. Perhaps the seven deadly sins? Pride in your ability forces you apart from your people (because D&D is all about a motley crew of miscreants). Greed leads you towards the loot. Sloth is deeper; while there’s the in-joke (can we sleep now? I need to heal up!), there’s also the “desire to retire.”
As Luke noted in his hacking thread, a Mouse Guard TC needs three things:
[ul]
[li]Team-based adventure. D&D has always had this.[/li][li]An implacable, over-arching force (of nature). The characters are points of light in a world of darkness, but the over-arching force generally changes per-campaign.[/li][li]Dramatic adventure that focuses on fighting for what you believe in. Another D&D staple. [/li][/ul]
I think conflicts are pretty well covered, though there should probably be one in there for traps. Hazards continue to include weather, wilderness (inc. dungeons), animals (monsters, inc. dragons), and mice (people). Territories depend on your setting; Forgotten Realms and Eberron are all ready for an easy conversion.
As for skills and abilities, they should be generally good, though minor renaming (for familiarity; perhaps health -> constitution, for example) might be nice. D&D 4.0 includes a bunch of backgrounds, which lead straight into traits and territory skills. Most D&Ders can handle the idea of wises as old-school “Knowledge (…)” skills, so that’s nice and easy to keep.
Fighter becomes a 4.0-style power source, which gives us fun things like Psionics and Arcane mages practically for free. Most of the other skills can stay as-is, and we’d take the Realm Guard changes for humanoid characters.
As noted, there should be a Trap conflict. The base can be Health or Nature, like a fight, but the test skill should be something like Scout (for noticing it) or Hunter (for disabling it). I’d rather have a skill like Thievery, but I’m not sure what it’d replace, or if it’d just be new. Perhaps a Trap-wise? Seems like a cop-out.