unlike tyrone, i won't venture a guess as to what your sexual orientation might be (and it's questionable whether cross dressing is protected as a "sexual orientation" anyway).
there are transgendered or transexual organizations that are independent from gay and lesbian organizations, and you can be, for example, a man dressing as a woman and consider yourself straight, or gay, or lesbian, or bisexual, ambisexual, celibate, or otherwise...
what you do in private should stay private and out of your career. in fact, in california, there's a new law that takes effect 1/1/2000 that prohibits employers from discriminating against employees based on what they do off-duty. some other states have similar protections. moreover, there are some localities (e.g., washington d.c., santa cruz CA) that have laws that prohibit "appearance discrimination."
and, in my employment-law experience over the last few years, i've encountered (in california) several companies who have successfully handled the gender-transformation of an employee (e.g., Dennis leaves on Friday and comes back Monday as Denise). the only worry has been the "potty issue" (i.e., which bathroom does a transgendered person use? -- and the Ally McBeal answer is: whichever they want), and it's never actually been a problem, only a worry.... and, according to your story, you're not even planning on dressing up at work.
so, stop worrying. i'm sure you look fabulous, both at work and at home. i bet your current employer doesn't care if you wear a cheerleader's outfit at home all weekend as long as you show up ready for work on Monday. the jerk that's ratting your secret is a jerk and a rat; that's life (of course, you could sue him for invasion of privacy (public disclosure of private facts)).