Also, before you started adding constraints, did you go into edit mode on your armature, select all bones, and do an alt-n to properly adjust bone roll?
:o
Yes.
I had the same problem in getting a (mech) leg to behave along a 2d plane.
I came up with a solution (no fancy bells and whistles) that worked well for me. It involves a couple of empties and restraining thier movements… I could explain it at great lengths, but a blender file says a thousand words, so here it is:
Hope this helps.
Thanks, bob_dog, it isn’t as self contained as harkyman’s idea, but it may just do the trick. 
All I need to do now is find out why editing ipo curves with bezier handles makes Blender freeze the system. (Perhaps it is time I ditched Win98 and used linux instead.)