Dunno what you mean by animated mesh, but boned/skinned characters and such can be exported as .X (DX8) and then converted to .B3D with Ultimate Unwrap for example.
http://www.softimage.com/download/xsi/converters/microsoft/default.htm
http://www.unwrap3d.com/formats.aspx
http://www.softimage.com/download/xsi/converters/microsoft/default.htm
http://www.unwrap3d.com/formats.aspx