As in any job interview situation, play up your strengths, and minimize (but don't hide) your weaknesses. Say "I don't have any formal Sybase training or experience, but I do have X years working with <foo> which I understand is very similar in practice. I do feel I'm very strong in your other requirements. I think those might allow me to contribute to your needs immediately, while I pick up what I need to know about Sybase." Give an example or two of what a fast learner you have been in the past when presented with other opportunities to learn a new technical skill or system.

Ultimately, though, if they think you need Sybase to be effective, and you don't have it, then you probably won't be effective, and what kind of job experience is that going to be?

(Of course, this is assuming that you get to the interview stage. If it's a big firm with HR drones set to filter resumes, you might not get that far. In that case, find someway to include Sybase in your resume, without making any false claims. Perhaps an entry like "Software currently studying: Sybase". And then be studying it.)