You can use <Run>Foo</Run> and place hte text stying in TextBlocks. For example:
<TextBlock>Hello <Run FontWeight="Bold">There</Run>!!!</TextBlock>
(If this has answered your question, "Mark as Answer")
Shawn Wildermuth
C# MVP, MCSD, Speaker and Author
Silverlight 2 Workshop
November 19-21, 2008 - Seattle, WA
December 1-3, 2008 - Dallas, TX
http://silverlight-tour.com