串口异步通信代码:如何在读取XML数据时实现搜索,来着分

chat.xml
<?xml version="1.0" encoding="GB2312"?>
<chat>
<user>
<ip>127.0.0.1</ip>
<client>主人</client>
<content>4</content>
<time>2006-6-12 15:23:38</time>
</user>
<user>
<ip>192.168.1.5</ip>
<time>2006-06-10 214:11:20</time>
<client>厂长</client>
<content>你好！</content>
</user>
</chat>

chat.xsl
<?xml version="1.0" encoding="gb2312"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
<table border="1" style="border-collapse: collapse" bordercolor="Teal" align="center" width="100%" height="34">
<tr>
<td valign="middle" align="center" bgcolor="Teal" height="85">
<font style="color:White;background-color:Teal;font-family:华文行楷;font-size:X-Large;font-weight:bold;">聊天室！</font>
</td>
</tr>
<xsl:for-each select="//user>
<xsl:apply-templates select="ip"/>
</xsl:for-each>
</table>
</xsl:template>
<xsl:template match="ip">
<tr>
<td height="26" valign="middle" align="left">
<font><xsl:value-of select='.'/> 对
<xsl:apply-templates select="../client"/> 说：
<xsl:apply-templates select="../content"/>
</font>
<font color="#cccccc">（<xsl:apply-templates select="../time"/>）</font>
</td>
</tr>
</xsl:template>
</xsl:stylesheet>

请问：
我想根据时间值time来挑选数据（如time>2006-06-10 214:11:20）时间值可以根据程序改变
如何做
下面是我写的函数

Private Sub ShowXml()
Try
'创建XmlDocument对象
Dim XMLDoc As XmlDocument = New XmlDocument
XMLDoc.Load(Server.MapPath("chat.xml"))
'创建XslTransform对象
Dim XSLTran As XslTransform = New XslTransform
XSLTran.Load(Server.MapPath("chat.xsl"))
Dim XMLNot As XmlNodeList = XMLDoc.SelectNodes("//user[time>='" & Session("Ntime") & "']")
Dim ms As MemoryStream = New MemoryStream
XSLTran.Transform(XMLDoc, Nothing, ms, Nothing)
ms.Seek(0, SeekOrigin.Begin)
Dim sr As StreamReader = New StreamReader(ms)
'显示结果
Response.Write(sr.ReadToEnd)
Catch ex As Exception
Response.Write(ex.Message)
End Try
End Sub
如何修改