and if not fixed maybe just singlespeed with a freewheel; a lighter cheaper way to go especially if your commute is mostly flat!

you could get back to your bmx roots without gears....

i'd go with a cyclocross frame all the way. and don't be afraid to try some different setups (for example: i prefer bullhorn bars to the typical road drop bars).

for tires i would find something puncture resistant and slightly wider than your standard skinny road tire (tires made for touring seem to be pretty durable). i run continental toptouring 700x28 which are pretty good but.... specialized aramdillos seem to be the benchmark for nearly flat proof tires. getting a sturdy tire is one of the most important things in my opinion cause nothing sucks worse than fixing a flat tire in crappy weather.

finally; fenders rule if you plan on riding in all weather conditions.