Play to your strengths, but give them an indication that you are willing and able to round out your knowledge in some new areas. In the area of software, you really don't necessarily want someone who has 20 years experience in every facet of the job being applied for. You want some solid foundation to build on, but you also want the job to challenge the applicant in some ways.

I always did better in interviews where I admitted there were some aspects in the job that I'd have to come up to speed on in rapid fashion. Makes the job a challenge for myself, and I come through with a positive attitude. Worst interviews I have is where the work looks easy - a depth of knowledge can scare the person doing the hiring. :-)