XceedStreamingCompressionLib.XceedStreamingCompression compressor =
                     new XceedStreamingCompressionLib.XceedStreamingCompressionClass(); 

compressor.License( @"your license key" ); 

compressor.CompressionFormat =
                        new XceedStreamingCompressionLib.XceedBZip2CompressionFormatClass();      

object sourceData = "This is the data to compress compress compress";      

try
{
  compressor.WriteFile( ref sourceData,
                        XceedStreamingCompressionLib.EXCFileProcessing.cfpCompress, true,
                        @"c:\test\file.cmp", false );
}
catch( System.Runtime.InteropServices.COMException except )
{
  MessageBox.Show( except.ToString() );
}

XceedStreamingCompressionLib.XceedStreamingCompression compressor =
                  new XceedStreamingCompressionLib.XceedStreamingCompressionClass(); 

compressor.License( @"your license key" ); 

compressor.CompressionFormat =
                        new XceedStreamingCompressionLib.XceedBZip2CompressionFormatClass();      

object bytesRead = null;

try
{
  object decompressedData = compressor.ReadFile( @"c:\test\file.cmp", 0, 0,
            XceedStreamingCompressionLib.EXCFileProcessing.cfpDecompress, true, ref bytesRead ); 

  MessageBox.Show( System.Text.Encoding.Unicode.GetString( ( byte[] )decompressedData ) );        
}
catch( System.Runtime.InteropServices.COMException except )
{
  MessageBox.Show( except.ToString() );
}