Anyone have a link or a book rec for how to use a screener?

So far in my investing life, I've used only index funds and mutual funs in the 401K. I'm looking at this market thinking it's time to get in, this may not be the bottom, but there are still good buys. I do plan to keep doing the VFINX, but am looking to supplement the growth a bit, if I can.

I've opened an account at Zecco.com, they have a screener, but to be honest, I can't figure it out. I looked at Yahoo, which is easier to start to use, but I don't know what I am looking for. Which of the various tools are going to give me the best result?

Thanks in advance

fredinseoul