Promoting Technical Users Groups?

An anonymous reader asks: "I'm trying to promote a technical user group in my area. We have great sponsorship and have had great speakers. I know my town has a lot of software developers employed, however I'm at a loss as to how to announce and get the word out to them. As a software developer working for a company, how do I get information to you? SPAM? Surely you delete those. Mail? I suspect my ad will never get beyond the mailroom. Should I post in bookstores? Put ads on the radio? Please help!"