from that link, apparently left handed has x in one direction, while right handed has x in the other. all i ever remember is the right hand rule for cross products, which means you align your index finger to one vector, your thumb to the other, and your palm points to the cross product vector.
i should hope that you shouldnt have to worry about which system they are, so long as you apply the same rules to all of them, it should work out. in all of my classes with vectors, we've never once mentioned a "left handed" system, from calculus to electrical engineering to computer graphics. always right hand rule.