I really try not to bother coworkers unless I'm totally stuck. They're all busy working on their own projects, and taking them out of the zone to help me doesn't seem fair, especially if they don't know the answer either because then I interrupted them for nothing.
The best way to ask a coworker for help: Look for a moment when he or she is not in flow that you will break. Returning from the water closet or coffee maker, or just if you happen to glance at their screen and see Gmail or HN or something.
(Yes, a programmer can be in flow while doing those activities, but the incidence rate is lower.)
