应CNET要求。把目录浏览类转贴过来。这个是几个月以前写的。（来自ASP.NET版）

using System;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace Blood.Com.ClassLib
{
    /// <summary>
    /// 目录对话框控件
    /// </summary>
    public class DirectoryDialog
    {
        [ StructLayout( LayoutKind.Sequential, CharSet=CharSet.Ansi )]
        ///<summary>
        ///浏览信息
        ///</summary>
        public struct BROWSEINFO
        {
            public IntPtr hWndOwner;
            public int pIDLRoot;
            public string pszDisplayName;
            public string lpszTitle;
            public int ulFlags;
            public int lpfnCallback;
            public int lParam;
            public int iImage;
        }

        private const int MAX_PATH = 260;
        /// <summary>
        /// 指定浏览类型
        /// </summary>
        public enum BrowseForTypes
        {
            /// <summary>
            /// 浏览计算机
            /// </summary>
            Computers = 0x1000,
            /// <summary>
            /// 浏览目录
            /// </summary>
            Directories = 0x1,
            /// <summary>
            /// 浏览目录和文件
            /// </summary>
            /// <remarks>只能工作于4.71或更高的版本<remarks>
            FilesAndDirectories = 0x4000, // 4.71版
            /// <summary>
            /// 浏览系统根目录
            /// </summary>
            FileSystemAncestors = 0x8
        }

        [ DllImport( "ole32.dll")]
        private static extern int CoTaskMemFree(IntPtr hMem);
        [ DllImport( "kernel32.dll")]
        private static extern IntPtr lstrcat(string lpString1, string lpString2);
        [ DllImport( "shell32.dll")]
        private static extern IntPtr SHBrowseForFolder(ref BROWSEINFO lpbi);
        [ DllImport( "shell32.dll")]
        private static extern int SHGetPathFromIDList(IntPtr pidList, StringBuilder lpBuffer);
        /// <summary>
        /// 显示公共文件夹对话框
        /// </summary>
        /// <param name="hWndOwner">文件夹对话框所有者</param>
        protected bool RunDialog(IntPtr hWndOwner)
        {
            BROWSEINFO udtBI = new BROWSEINFO();
            IntPtr lpIDList;
            GCHandle hTitle = GCHandle.Alloc(Title, GCHandleType.Pinned);
            // 设置WINDOWS的所有者
            udtBI.hWndOwner = hWndOwner;
            // 设置WINDOWS的所有者
            udtBI.lpszTitle =  Title;
            // 设置WINDOWS的所有者
            udtBI.ulFlags  = (int)BrowseFor;
            // 创建一个字符串缓冲用来显示名称
            StringBuilder buffer = new StringBuilder(MAX_PATH);
            buffer.Length = MAX_PATH;
            udtBI.pszDisplayName = buffer.ToString();
            // 显示浏览目录对话框
            lpIDList = SHBrowseForFolder(ref udtBI);
            hTitle.Free();
            if (lpIDList.ToInt64() != 0)
            {
                if (BrowseFor == BrowseForTypes.Computers)
                {
                    m_Selected = udtBI.pszDisplayName.Trim();
                }
                else
                {
                    StringBuilder path = new StringBuilder(MAX_PATH);
                    //从lpIDList中取得路径
                    SHGetPathFromIDList(lpIDList, path);
                    m_Selected = path.ToString();
                }
                //释放内存
                CoTaskMemFree(lpIDList);
            }
            else
            {
                return false;
            }
            return true;
        }
        /// <summary>显示公共文件夹对话框</summary>
        public DialogResult ShowDialog()
        {
            return ShowDialog(null);
        }
        /// <summary>Shows the common folder dialog.</summary>
        /// <param name="owner">The owner of the folder dialog.</param>
        public DialogResult ShowDialog(IWin32Window owner)
        {
            IntPtr handle;
            if (owner != null)
                handle = owner.Handle;
            else
                handle = IntPtr.Zero;
            if (RunDialog(handle))
            {
                return DialogResult.OK;
            }
            else
            {
                return DialogResult.Cancel;
            }
        }

        /// <summary>
        /// 指定对话框的标题
        /// </summary>
        /// <value>对话框标题</value>
        /// <exceptions cref="ArgumentNullException">当值为null（VB.NET为Nothing）时抛出错误</exceptions>
        public string Title
        {
            get
            {
                return m_Title;
            }
            set
            {
                if (value == null)
                    throw new ArgumentNullException();
                m_Title = value;
            }
        }
        /// <summary>返回选择的项目</summary>
        /// <value>选择的项目</value>
        public string Selected
        {
            get
            {
                return m_Selected;
            }
        }
        /// <summary>指定浏览类型</summary>
        /// <value>浏览类型</value>
        public BrowseForTypes BrowseFor
        {
            get
            {
                return m_BrowseFor;
            }
            set
            {
                m_BrowseFor = value;
            }
        }
        //申明私有变量
        private BrowseForTypes m_BrowseFor = BrowseForTypes.Directories;
        private string m_Title = "";
        private string m_Selected = "";

        /// <summary>
        /// 构造函数
        /// </summary>
        public DirectoryDialog()
        {
            //
            // TODO: 在此处添加构造函数逻辑
            //
        }
    }
}