a fridge compressor work pretty good for a cheap vacuum pump, http://www.berkut13.com/sucker.htm details one used for doing composite work for full size aircraft. I found this site on vac bagging http://www.pilotsguide.com/rc/vacbag.shtml it gives the general idea on how it works. www.joewoodworker.com also has some good vac bagging info.

Darren