I love the idea of a "geek" themed party! Everybody gets pocket protectors or mouse pads as favors!
You could decorate with scientific symbols and equations... or computer motherboards.
Could you do some sort of joke by making a square pie with a letter R on it for "pi R squared"?
There's a lot of fun slogans you could use in decorating, at the Mental Floss t-shirt store:http://www.mentalfloss.com/store/T-Shirts
And could you get ahold of a broken keyboard and pry the letters off to decorate with those also? (Maybe spell geeky words and phrases with them.)
Play some sort of Trivia game as an activity.