Microsoft.Office.Interop.Excel.Application oXL = new Microsoft.Office.Interop.Excel.Application();
if(oXL.Version.Equals("15.0"))
{
   //bla bla..
}
else if(oXL.Version.Equals("14.0")||oXL.Version.Equals("12.0") || oXL.Version.Equals("11.0"))
{
   //bla bla..
}