Do you use Internet Explorer 7 by any chance? There's a setting in this version that is turned on by default, where if what you want to print is too wide, IE will reduce everything so it does all fit on one sheet of paper - of course, making the text incredibly small in the process.
One way round it is to try and print landscape and see if it comes out any bigger. There are a couple of other settings you can change, but I can't remember what they are to hand (I originally came across this problem at work and I'm at home at the moment).