Promoting Linux always seems to be tough. I find that it's a little difficult to spread the word about an operating system; even if it is free and stable and wonderful and will get you the hottest woman on the face of this planet who will worship the ground you walk on and... sorry got a little carried away.
I do not do promotion for the GA Ubuntu team, but here are some things you might consider. Pamphlets are always good, so are some free CD's. A movie night may be in order, with the intent of sharing a distribution, booklet, etc. Of course a movie themed about computers might be a good idea but not absolutely necessary.
LAN parties / demonstrations using some free FPS games for Linux? The Install Fest you mentioned. Advertising in the newspaper, a short cable video ad can help, but will cost a little. What about setting up a local website for it?
Getting ideas from non-profits can be a good idea; like Churches and assistance programs. These guys have been promoting for a long time and usually without a lot of finances; though religion is a bit easier to get a following in, I think.
I get stumped around about here as I cannot think of anything else that will get people into it or simply interested. Though you are dealing with an educated crowd, it'll probably be easier for you.
One idea I had that gave my local LUG a good laugh, was a project to build a kiosk of some type using Linux as a promotional platform. The idea was a get together kind of hands on project that would be a team builder and still end up with a good enough product to spread the word on Linux. It's been done before; in fact I believe Ubuntu has free plans for one out there.
I know some were made for Katrina to help locals get back online and in touch with family members, but what distro they used, I'm not sure. They can be quite useful. Maybe a bit ambitious, but remember it's just a big wooden box with a computer inside.
Look for "KDE Kiosk Admin Tool", KDE Kiosk Mode Guide (http://developer.kde.org/documentation/tutorials/kiosk/index.html), using Firefox or Opera in Kiosk mode, Kiosk Appliance (https://launchpad.net/kiosk) and the plans, but I cannot find them right now.
One other thing, it's so much easier if you have even one other person to make it more of a "group" than if it's just you. This is the hardest part; getting that one other person. Depends on your locale though.
Good luck! And let us know what you came up with / used. Jean-Claude