Where can i get a job for only 3 weeks?

Against my wishes, I have to go on a family trip this summer when I can be working and making money for university. When I get back, I will only have 3 weeks to make money. Does anyone have any ideas? I am 18, male, very good with computers, worked for over a year as a pc salesman at futureshop, and am almost willing to work anywhere to maximize the money I can make.