Internationalized Domain Names, or IDNs, are web addresses in your own language. Until now, browsers and email clients did not support the use of IDNs. There are some internet browsers that support this.

Camino for MacOS X (nightly, not 0.7)
Firefox 0.8 or later
Mozilla 1.4 or later
Netscape 7.1 or later
Opera 7.22 or later
Safari 1.2 or later for MacOS X

If you use another browser (f.ex Microsoft Internet Explorer) you probably need to install this patch to use these types of domains http://www.idnnow.com/index.jsp?lang=en.