How to avoid wrong display of "umlaute" (only in Internet explorer)

Hello,

I found that my (german) site white-label-ebooks.com has a problem with “Umlaute” (ä, ö ü,) but only on Internet Explorer….

Für example “ü” turns into “Ã1/4” …:

http://screencast.com/t/9u9hlwVukwy

Does someone know why this happens (only in IE),

and how to fix this?