>Is this like a weaker version of Trapping? Weight of weapon
>effects damage?

Yes, that's about correct. If you think of it that way you'll generally draw the right conclusions.

>If its like trapping, does it stack with
>trapping?

It does, but there are some diminishing returns. For example (all totally made up numbers) if in a given situation Trapping alone would give you 50 damage and AO alone would give you 20 damage, the two together might give you 60 damage.

That being said, if you're picking trapping and you're already committing to that kind of gearing strategy you might as well pick up AO too.