Ok, I just tested your site and 4 other Mint sites in IE8.
Your user is correct in that your site is showing some very weird behaviour in IE8 on our test browser. The whole screen is sliding from the right and half is missing.
All other Mint sites, including our demo work fine in IE8. So my guess is that some of your customisation is causing the issue. It may be a missing or unclosed html tag, looking at the kind of problem that is showing.