I guess to a large degree this could depend on how out you are or if you are in transition/going full time. Now I'm not how it works in Australia Carol, or in the US, but in Canada employers are prevented by law from asking questions such as are you, or or do you plan to become pregnant. An employer would want to know this for obvious reasons. The applicant can divulge this info if she wants to but she is not compelled to.
I believe that before anyone in our position applies for a job that they should do some investigation before hand, find out what their policies are on discrimination, and benefits, is it an open company, has there been other applicants who have gone before, and were successful etc. then make a decision from there. I know that some of the info may not be available but it's worth a try as you have nothing to loose.
If you feel the company would discriminate against you then I would advise that this company would not make a great employer and should be avoided, as what would be the point in withholding that you are TS and plan to transition if you know that the company doesn't have a great track record, and would make you miserable.
Personally, I would do my homework, find a company that does things right, and be open and up front. If you added that being TS would not interfere with your employment and it would enhance your performance, making you a better employee I think the right employer would hire you, provided that you met all the other requirements.
In the end it all comes down to the interviewer(s) and how they personally feel. Regardless of company policy you may be discriminated against and you wouldn't know it, and not just for being TS, you can be discriminated because you are male or female, your skin colour, because you are overweight, you have one leg...
Steph