Internet Explorer 7.0 Problem

There are several users at my Company that use the U.S. Airways web site to check and book flights. Internet Explorer 6 works fine – no problems. However, I have upgraded some workstations to I.E.7, and now, when they search for flights, they get the message about I.E. encountering a problem and needing to Close. I tried going back to I.E.6, and when I do that, the U.S. Airways home page opens, but I.E. completely crashes when the “Search” is clicked. I’ve cleared the temporary internet files, etc., and still have the same problem – now I’m completely STUCK! NEITHER I.E. works! HELP!!! Microsoft wants $245.00 to correct their problem.