多线程效果不理想！HELP ME!!!

[平台想钱想疯了]

While True
Dim TargetUrl As String
Dim TargetContent() As [Byte]
TargetUrl = Me.TxtBoxDomain.Text
Dim BeginTime As Integer = System.Environment.TickCount
Dim EndTime As Integer
Dim strURL As String = TargetUrl 'Me.TxtBoxDomain.Text
Dim WebRequest As WebRequest = WebRequest.Create(strURL)
Dim WebResponse As WebResponse = WebRequest.GetResponse
Dim ReceiveStream As Stream = WebResponse.GetResponseStream
Dim encode As Encoding = Encoding.GetEncoding("GB2312")
Dim readStream As New StreamReader(ReceiveStream, encode)
Dim read(256) As [Char]
Dim count As Integer = readStream.Read(read, 0, 256)
Dim TempStr As String

While count > 0
Dim str As New [String](read, 0, count)
TempStr += str
count = readStream.Read(read, 0, 256)
End While

EndTime = System.Environment.TickCount

readStream.Close()
WebResponse.Close()
Thread.CurrentThread.Sleep(30)
i += 1
End While


以上为我写的多线程调用的主要执行代码部分,我其中TempStr中获取得到的是对一个网址的返回结果信息,也就是在访问http://www.xxxx.com/的结果,我在测试中起动了300个线程那他们不停的工作,虽然主机的CPU上升到了100%的样子,可访问对方的WEB服务器,打开网页,速度没有太大的影响,仍然能正常访问,这是为什么呢?我一同用JAVA写的多线程的,才不到100个线程对方网页就已经是打开很慢很慢的了,WHY???请各位指点一二!!!谢谢!!!如何改进??