Get rain gear. Put lights on your bike. Change into work clothes once you've arrived. Some jobs are more friendly to biking than others, but with some planning, you can make it happen. Also, be very aware where the bad traffic and rough neighborhoods are.
Spend a little extra money on a decent bike. I bought my self a mountain bike so that I could try a little off-roading on the weekends, and wondered by so many bikes were over-taking me. Then I realised. They all had light racer style bikes. They were literally zooming past me with hardly any effort.