Hi Elmar,
Got this tip from Rosemaryl.
You have to be careful of placement as the html tags must be inside of text indicators " ". You can start them in one and end them in another, but to accomplish this one I had to add them:
Format the formula field, paragraph formatting tab, Text Interpretation: HTML Text and perform the following:
"<B>" & totext(minimum({?Parameter})) & "</B> to " & "<B>" & totext(maximum({?Parameter})) & "</B>"
Jacque