When I generate a BIRT report in SilkCentral Test Manager the data contains all of the HTML formatting tags.
Below we see a report preview which contains HTML tags in the Requirement Description.
The solution is to open the BIRT report designer, select the Layout tab, then Properties | General | Content Type. Content type is normally defaulted to Auto; set this to HTML and it should resolve the display problem in SilkCentral. You can check by selecting Preview in BIRT.