Well, Katrina, two weeks have gone by and nobody's answered. I don't know the answer but I'm going to have a guess that may be helpful in you working it out for yourself.
When I downloaded the latest version of Firefox the other week, it gave me a spiel about the new FF not needing some plugin to view videos. I'd guess the latest IE (IE8) would have the same.
So I guess the video format that you have used in your website (uploaded to U-Tube) is such that it can be read by your browser at home but not the older browser.
Hope that's of some help!