VS2008 找不到System.Drawing命名空间

这个例子是MSDN里面的，我想用一下，结果说找不到命名空间！
using System;
using System.Drawing;
using System.Drawing.Imaging;
class Example_SetJPEGQuality
{
public static void Main()
{
Bitmap myBitmap;
ImageCodecInfo myImageCodecInfo;
Encoder myEncoder;
EncoderParameter myEncoderParameter;
EncoderParameters myEncoderParameters;

// Create a Bitmap object based on a BMP file.
myBitmap = new Bitmap("Shapes.bmp");

// Get an ImageCodecInfo object that represents the JPEG codec.
myImageCodecInfo = GetEncoderInfo("image/jpeg");

// Create an Encoder object based on the GUID

// for the Quality parameter category.
myEncoder = Encoder.Quality;

// Create an EncoderParameters object.

// An EncoderParameters object has an array of EncoderParameter