You can make custom tag for this. You find information about how to do that here: http://www.ez.no/ez_publish/documentation/customization/components/datatypes/ezxmltext/custom_tags
You need to use the HTML entity to display the em dash if you are not using any of the following codepages:
adobe-standard-encoding
cp874
hp-roman8
macintosh
next
windows-1250
windows-1251
windows-1252
windows-1253
windows-1254
windows-1255
windows-1256
windows-1257 windows-1258
If you use any of those codepages you can also just use the character directly.
Zoltan, that is not possible to do. We do not allow special characters to be inserted into the forum and the characterset here on ez.no is latin1--which does not support em dash.