public string GetNetCardMacAddress()
        {     

           ManagementClass mc = new ManagementClass("Win32_NetworkAdapterConfiguration");
           ManagementObjectCollection moc = mc.GetInstances();
            string str = "";
            foreach (ManagementObject mo in moc)
            {
                if ((bool)mo["IPEnabled"] == true)
                    str = mo["MacAddress"].ToString();
            }
            return str;
        }

------解决方案--------------------

网卡注册也可能重复
通过硬盘序列号，加密生成用户号
否则使用序列号，在线注册


------解决方案--------------------

这是一本书上的一个网卡注册的完整例子，你可以看看

C# code
using System; 
 using System.Collections.Generic; 
 using System.ComponentModel; 
 using System.Data; 
 using System.Drawing; 
 using System.Text; 
 using System.Windows.Forms; 
 using System.Management; 
 using Microsoft.Win32; 
 namespace Ex16_09 
 { 
   public partial class Form1 : Form 
   { 
     public Form1() 
     { 
       InitializeComponent(); 
     } 
     string[] strLanCode = new string[12];// 网卡信息存储到 
     string[] strkey ={ "Q", "W", "7", "E", "D", "F", "2", "G", "R", "T", "Y", "8", "P", "N", "B", "V", "C", "X", "Z", "0", "9", "I", "8", "6", "U", "O", "P", "M", "5", "4", "3", "1", "A", "S", "H", "J", "K", "L" }; 
     //生成注册码 
     public int intRand = 0;//判断随机生成次数 
     private void button1_Click(object sender, EventArgs e) 
     { 
       //把网卡信息转换成字符串 
       string strCode = GetNetCardMacAddress();//调用函数获取网卡信息 
       strCode = strCode.Substring(0, 2) + strCode.Substring(3, 2) + strCode.Substring(6, 2) + strCode.Substring(9, 2) + strCode.Substring(12, 2) +strCode.Substring(15, 2); 
       string strb = strCode.Substring(0, 4) + strCode.Substring(4, 4) + strCode.Substring(8, 4);//把网卡信息存储到 
       for (int i = 0; i  < strLanCode.Length; i++)//把网卡信息存入数组 
       { 
         strLanCode[i] = strb.Substring(i, 1); 
       } 
       Random ra = new Random(); 
       switch (intRand)//随机生成注册码的顺序 
       { 
         case 0: 
           label5.Text = strCode.Substring(0, 4) + "-" + strCode.Substring(4, 4) + "-" + strCode.Substring(8, 4) + "-" + strkey[ra.Next(0, 37)].ToString() + strkey[ra.Next(0, 37)].ToString() + strkey[ra.Next(0, 37)].ToString() + strkey[ra.Next(0, 37)].ToString(); 
           intRand = 1; 
           break; 
         case 1: 
           label5.Text = strCode.Substring(0, 4) + "-" + strCode.Substring(4, 4) + "-" + strLanCode[ra.Next(0, 11)] + strLanCode[ra.Next(0, 11)] + strLanCode[ra.Next(0, 11)] + strLanCode[ra.Next(0, 11)] + &quo