If you really do want to bike commute, then I would suggest just generally adding some urban riding into your routine. I got used to riding in traffic by following the route used for the Broad Ripple/Butler weekly training ride route "hosted" by CIBA. It is marked so you could follow it on your own.

Some of CIBA's dinner and weekend routes would be good for that purpose, too. I would start there before doing a weekday commute into downtown.