I don't believe that just anybody can post something that gets filed under the jobs tab. I think that's limited to YC associates, and I don't think that's likely to change (although pg could certainly change his mind).
Honestly, there's nothing stopping you from posting a job posting yourself as a normal submission, but I'm not sure that's best for the board. There's already a lot of noise on the board, and I'm not sure additional job posts are going to help that problem.
There's a "Who's Hiring?" post that happens on the first of every month, and that's probably your best bet.
