非要自己写。
算了。。大家自己看看吧。。不过我还是喜欢使用API。嘿嘿

目录选择对话框类
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
//
}
}
}