>Does the system on the B744/B767 prevent skids?
No system "prevents" skids. Virtually all airliners have an anti-skid system which _attempts_ to prevent skids. Usually works quite well.
>...but the Qantas incident in BKK proved that the plane could aquaplane?
See comment above.
>Is reverse thrust usage limited in crosswind conditions due to the fact that
>the plane would start to weathervane into the wind and reverse side force
>component adds to the crosswind component and drifts the airplane to the
>downwind side of the runway?
Some aircraft have limitations on the use of reverse thrust. Usually found on tail-mounted engine models. AA limits MD80 reverse thrust to (I think) 1.3 EPR, but F100 had no limit (reverser doors are blocked to provide limited amount of forward thrust at all times). B737/757/767 all are permitted unlimited reverse thrust use.
>Is there a very noticable directional control if one of the reverse fails to work espcially on twins?
Yes! Especially if failure occurs after deployment at high reverse thrust setting. Gets a bit exciting for a couple of seconds.