ranger's choking gas skill?

http://wiki.guildwars.com/wiki/Choking_Gas

Does this mean foes can't cast spells for the entire duration of the choking gas? Or just the next spell they cast?

It means if you hit them while casting the spell, they'll get interrupted. It doesn't mean they can't cast, you actually have to hit them to interrupt the spell they're currently using. That's what interruption means in general.

Ok rephrased: Does this mean foes spells are interrupted for the entire duration of the choking gas? Or just the spell they were casting when first hit?

I want to know if it's a one-shot interruption, or do I need to keep spamming arrows at them to interrupt their spells.

When Choking Gas is up, every arrow you use interrupts your target's (and adjacent foes') spells upon hitting them. Interestingly, it also interrupts if the arrows are blocked.

As a result, it's a good idea to use a stance like Lightning Reflexes or Flurry after you use Choking Gas so that you can fire at a caster quickly and interrupt a lot of spells. The caster is then compelled to find a wall or other obstacle to hide behind for shelter.

It might also be useful to use Practiced Stance to keep it up indefinitely.

exactly...each hit will cause an interrupt for the duration of the preparation. I used to use concussion shot for single target interrupt spamming. It worked well to shut down any caster boss. Basically I had marksman's wager, penetrating attack, sundering attack, needling shot, and concussion shot. The whole point would be to daze the foe with concussion shot and then spam penetrating and sundering attack until they were below 50% then finish them off with needling shot. Although it didn't have the AOE interrupt it was very good at shutting down a single target. A bit off topic I know but thought I would share just the same. Here is the template code
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