In a message dated 9/11/99 11:23:17 AM Mountain Daylight Time, 
alhuang@hcs.harvard.edu writes:

2. -kun
   This is used to address people of a lower or same station as yourself,
 in a clearly defined hierarchy. For example, a boss talking to an
 employee would likely use "-kun" when addressing the employee. An
 upperclassman in school would use "-kun" when addressing a lowerclassman
 (please refer to the "-sempai" tag defined later).  Note that there is
 no gender specification here--a male or female worker speaking to a
 junior female coworker may well use "-kun". It is also often used
 between good male friends, or from female to male friend, of more or
 less equal stature. To be used carefully.
 

just a side note... in most of the situations I have seen and leaned from, 
although kun is not specific to gender, it's uncommon to attach kun to a 
female... it may be more common than I think, but I'm not in Japan and 
surrounded with everyday situations, so I can't speak as an expert, only with 
what I have experienced when dealing with the Japanese culture; anime and 
otherwise.