I really don't recommend either I dont guess. Before or after, doesn't really matter. I just do all of my weights, and that type of stuff on different days than my cardio, so I wouldn't really know.
I would do em after, reason is if you over exert yourself with the situps than you realy won't be able to run.. maybe though you could warm up your abbs like with a lite workout than run than do some more latter.
Then I had a problem getting motivated, so she had me do them before hand, just as I was waking upin the morning, while still in bed if I had to, she said as long as I got them done it was all good!
I'd say after. If you run first it will pre tier your abs, giving better results. If you do abs first, you will not be able to run as fast and may in fact cramp up, degrading your cardio work out. All around after just works better. Believe me, I know from extensive experience.
I usually do ab work about 3-4 days a week, and if I do them on the day I run, I do them afterward. I think it depends on how intensely you run. I run 4-5 miles pretty hard (for me) with my wife, who ran X-country and track in college (while I was a couch potato). So I don't want to do anything to tire myself out before the run.
never target a specific muscle group until you are warmed up. You can tear something. your muscles need to be warm so you can avoid injury, plus, you can usually lift more, do more, or whatever.