Thanks to all for the very helpful replies and links to schematics. I'm
still sorting through the advice, but I'm pretty sure the problem lies
with the biasing of the opposed bases. (I had the same value resistors
connected to all bases).

I also am not providing a higher voltage for the upper pair of
transistors...

As far as mosfets I'm not really sure how to do this, I'm relatively new
to digital electronics and largely self taught (could you tell?)...
never worked with anything but NPNs and PNPs.

To answer a few questions, I'm using four NPNs.  And no I don't intend
to really deliver 10watts, although I implied that - I just happened to
have a big resistor around and tried it as the load.

The motors I'm controlling are actually quite small (yanked from small
toy RC cars). And the 122s are definitely overkill (they will be
replaced with much lighter weight transistors - not sure which yet).

I do know of off the shelf h-bridges but the cost I've seen per unit is
too much. I only intend to build a few of these.

Thanks again for the help,

Andrew