I broke into the Argonian Assemblage in Windhelm a long, long time ago, and got the quest to retrieve the double-distilled skooma. Got the stuff, went back, and all anyone said was that I wasn't supposed to be in there. Now, many days and hours of play (and months of game time) later, they're still saying it. Is there a way to reset them, presumably a console command, so I can turn in the quest?

argh, bump. This problem is annoying as hell.

find your quest here: http://www.uesp.net/wiki/Skyrim:Quests

then use http://www.uesp.net/wiki/Skyrim:Console and http://www.uesp.net/wiki/Skyrim:Console commands to advance it as necessary.