I haven't looked back through old NMA stuff or whatever to know if this is a known problem, but I never had it when I played back through in the day - I can't get the shooter to attack Killian after I talk to him, which seems to be messing up my quest line in Junktown. Are there conversation paths you can take that cause the guy to just stand in the store and never attack, or did something break here?

Not sure, I didn't have any problems with getting him to attack, did you go through all the options about problems and such with the lawman in charge?
I did that out of old habit, so I'm not sure if there's some specific thing you need to ask or not, but as far as the gang goes you need to trigger it, so I suspect the same's needed with this. (at the same time it's weird that he appears if you haven't triggered the sequence....)

Yeah, I guess I do trigger something, cause he comes wandering in. He just never attacks. Ansob's post worked, though, I just unloaded into his head from 5 feat and Killian thanked me for helping him.