Keith,
I have a similar situation in that prior to last year I was strictly a computer tech and had not installed one single camera in my life. My best business client asked me about camera systems and I initially told them I knew nothing about them. After sitting-in on their first meeting with a very 'slick' security salesman, I decided to look further into the video world. I quickly realized that the modern IP camera systems were nothing more than computer networks with cameras at the end of the cable instead of PC's, and was pretty sure I could adapt my computer skills to video.
After doing a huge amount of research (thank you IPVM), I discussed the idea of doing my first video installation for them. My approach was basically "honesty is the best policy". They knew up front I was learning and that there might be some hiccups, and I kew they were taking a chance with me, so I made it worth their while financially so that I could "learn on the job".
I'm not going to lie, the thought of accepting the responsibility of designing and installing a 30+ camera system in a industrial type business as my very first job was a bit un-nerving. However, the beauty of a relationship like this can be a win-win situation for both client and integrator. The client gets a known, trusted person to do the work and usually gets more personalized service to boot, and for the newbie integrator, well he gets his first job under his belt and gets paid (albeit not top prices) to boot.
I now have them up and running with a custom server running a VMS and 15 cameras so far. Although I have a long way to go, thanks to this job and again IPVM, I no longer consider myself a newbie and have self-promoted myself to Rookie! My clients are extremely happy with the end product and even though I'm not even finished with their job, they have started recommending me to their business colleagues.
In the end, as long as you feel confident in your abilities and your potential to learn, this kind of partnership is a win-win for you and your client. Number one thing though is to be open, frank, and honest with them so both sides know the situation and expectations are aligned.
Hope this helps.