I have the same problem with IE 8, so I use Firefox to take the PR tests. I haven't bothered to call their help desk, though I've heard they're incredibly helpful (for PR students, at least).
Their entire site is weirdly buggy, too. You often have to reset cookies to even get the main site to load. Maybe give that a shot, but I don't think it's going to work.
Either way, it's really dumb that it says IE 6.0+ is required but then tells you IE 8 is not compatible.