aligning to curves...

[psychostyrene]

can anyone please sugest to me some tools for aligning nulls and objects not to PATHS, but to CURVES....CurveConstraint will certainly do this but allows no options for cycling, movement in reverse, or any other kind of variation? i need have a looped curve which needs to have nulls travelling in BOTH directions along its length, and looping when they hit the end. the reason i must go with curves instead of paths is that the curves need to deform with the animation and obviously this is not possible with paths...

any help greatly appreciated
cheers