Here are some resources that may be useful to employers of employees that are undergoing a gender transition.
World Professional Association for Transgender Health
The World Professional Association for Transgender Health (WPATH, formerly known as the Harry Benjamin International Gender Dysphoria Association, Inc. (HBIGDA)) is a professional organization devoted to the understanding and treatment of gender identity disorders.
WPATH Standards of Care is where you can find the “standards of care” for the treatment of gender identity disorder. (Don't get lured by the “Click here to order” near the top of the page; there is a also a free download farther down the same page.)
Center for Gender Sanity
The Center for Gender Sanity is a consulting service for transsexuals and their employers. Much of the content on the site is a little bit dated, but there is still some useful resources there: