For Americans:

http://www.mental-health-today.com/gender/work.htm

she mentions simply circulating a memo to all fellow workers that the person will be transitioning on a certain date.  this is almost the same as putting note on notice board that I did.
advantange of being open about it is that no-one can complain they don't know they have to use the new gender and name.

A notice was posted in our lunchroom, while I was on vacation.  Upon my return I was full time and the store employees were informed.