Hmmm, it may not be for you then. I'd still check it out though...you never know. The one I am in and the ones that the School of Rock do are about learning to play in a band.
I had played in a band way back in high school, but never in front of an audience. Then I played in a church group. So I wasn't a total newbie to the whole thing. For me it was about getting in front of people and playing and improvising.
Anyway,. the thing they are doing could be totally different - check it out. Certainly worth a phone call.
As far as what to expect - expect people from various backgrounds, ages, and musical tastes. Expect it to take a bit for everybody to gel and get the groove going.
Alternatively, you could check out some of the websites that are out there, like BandMix. Before hooking up again with my music school group, I was seriously considering putting myself out there. It is www.bandmix.com.
Good luck!!