我先建了一个ConnToDB模块
Imports System
Imports System.Data
Imports System.Data.SqlClient
Imports Microsoft.VisualBasic

Module ConnToDB

Public ConnStr As String = "workstation id = user;packet = 4096;user id =;"
Public ConnectStr As String = ConnStr & "data source = 'zc401';persist security info = True;initial catalog =DLB"

Public DataAdapter As SqlDataAdapter
Public DataConnection As SqlConnection
Public DataSet As DataSet
Public Indexs As Integer
Public pepdom As Integer
Public No As String

Public Function GetDataFromDB(ByVal sqlstr As String) As DataSet
Try
DataConnection = New SqlConnection
DataConnection.ConnectionString = ConnectStr
DataAdapter = New SqlDataAdapter(sqlstr, DataConnection)
DataSet = New DataSet
DataSet.Clear()
DataAdapter.Fill(DataSet)
DataConnection.Close()
If Not DataSet Is Nothing Then
Return DataSet
End If
Catch
Return Nothing
End Try
End Function

Public Function UpdataDataBase(ByVal sqlstr As String) As Boolean
Dim sqlconn As New SqlConnection(ConnectStr)
Try
Dim cmdTable As SqlCommand = New SqlCommand(sqlstr, sqlconn)
cmdTable.CommandType = CommandType.Text
sqlconn.Open()
cmdTable.ExecuteNonQuery()
sqlconn.Close()
Catch
Return False
End Try
Return True

End Function
End Module

下面是登录界面代码：
Public Class Form1
Inherits System.Windows.Forms.Form

Public sqlstr As String = ""
Public strID As String = ""
Public pwd As String = ""
Public DS As DataSet

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

strID = Trim(Me.TextBox1.Text)
If strID = "" Then
MsgBox("请输入登录的用户名")
End If
pwd = Trim(Me.TextBox2.Text)
sqlstr = "select * from DLB where (用户名 = '" & strID & "')"
DS = New DataSet()
DS.Clear()
DS = GetDataFromDB(sqlstr)
If DS.Tables(0).Rows.Count > 0 Then
sqlstr = "select * from DLB WHERE (用户名 = '" & strID & "')AND(密码='" & pwd & "')"
Dim myDs As DataSet
myDs = New DataSet()
myDs.Clear()
myDs = GetDataFromDB(sqlstr)
If myDs.Tables(0).Rows.Count > 0 Then
pepdom = myDs.Tables(0).Rows(0)("权限")
Main.Show()
Else : MsgBox("密码不正确,请重新输入!")
Me.TextBox2.Text = ""

End If
Else
MsgBox("查无此人，请确认是否有该用户存在")
Me.TextBox1.Text = ""
Me.TextBox2.Text = ""
End If
End Sub

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
Me.Close()

End Sub
End Class

运行显示“未将对象的引用设置到对象的实例”错误，程序就无法进行了，请高手帮帮忙，做毕业设计，急啊！！！！

If DS.Tables(0).Rows.Count > 0 Then
sqlstr = "select * from DLB WHERE (用户名 = '" & strID & "')AND(密码='" & pwd & "')"

这步往下执行就出现异常了

谢谢5楼，遇到的错误解决了。但是它没有读数据库中的数据，无论我输入什么，它都显示“查无此人，请重新输入！”请问这是什么原因?谢谢！！！！

我建了用户表了，可就是连不上。还有就是我用的机器不能进行调试，每次显示“试图运行项目时出错：无法启动调试。绑定句柄无效。”这又是因为什么？？？拜托各位高手了

我知道不能访问数据库,是因为DataSet is nothing.但在模块中我已经定义了呀,那为什么还是空呢?谢谢!!!!!

应该是数据库没连上的缘故，我单步执行了 走到这步DataAdapter = New SqlDataAdapter(sqlstr, DataConnection)就不行了。点开DataConnection查看有这个显示ServerVersion = {"无效操作。连接被关闭。"}。好像是数据库驱动程序的问题，
该怎么解决？

能。
你qq开吗？
我想细问一下
我加你了

呵呵，小妹的问题已经解决了。是在数据库连接时我的设置有问题，而程序本身是没错的。谢谢各楼的关注与帮忙。希望以后还能继续讨论！特别感谢14楼的"为记忆上锁"