Okay, here's what honestly worked for me:
I spoke with the secretary of a PI who was working with general technologies and field I was interested in (Genetics) and set up a meeting, this was after several failed attempts via e-mail and direct contact with him. I asked her also how outgoing and approachable he is, and also spoke with some of the people in his lab.
Anyways, I ended up going to meet with him. Sat down, asked how he got into genetic research, about his path into research, etc. Then I was just really candid with him that I wanted to work in his lab, at least in a voluntary capacity.
He asked what I wanted, I explained my interests and plans (and offered to start off with lit review of his recent publications and publications of his choice on the topic I was to work on). We met a week later and started training.
It helps if you choose something you're really excited in, because it shows, I think. I was talking with him about one of his interviews with Science magazine, and microarray technologies and how the early applications in diagnostics and how they blew my mind away, etc. So I think, I hope, he got a feel of how motivated and excited I was to work with him.
I suggest something similar. You have nothing to loose, so find someone you would like to work with, do some basic asking around about how they are as a person (professional, laid back, stern, easy-going, etc) and then go meet with them and be frank about what you hope to gain and give.