I wanted to save solid works 2011 files , such that it can be opened in Solid works 2008, without loosing its features data like fillet , and other features
No, SolidWorks is not backwards compatible. Once a file has been saved in SolidWorks 2011, it cannot be opened in SolidWorks 2010 unless it is exported as a neutral file (i.e. Parasolid). Note that when importing a neutral file all feature data history is NOT included.