The Incredibots servers are back up now so I can give you a link to my walking machines.
Quadrapod: http://incredibots.com/?robotID=dali...31c04.54213413
Hexapod: http://incredibots.com/?robotID=dali...b3a39.03183432

Both only need four motors to move and they would both use the same walk cycle programme (see instructions in game.) If you look at one side of the walk cycle for the hexapod (red or blue legs) then you can sort of see how it would turn using normal tank steering. Invertability is relatively simple with the hexapod, just extend the legs out the top.

The Quadrapod one is only one side of it and two of those would be needed for tank steering. I believe it to be a more solid machine with more grip, however, it would be far more difficult to make it invertible without complicated shafts that go through one another (at the moment I would be placing motors on top of the leg.)

I hope you enjoy my long, ever so slightly mad ramblings about walking robots.

JB