eclipse与数据库连接的错误

菜鸟问题，暑假刚学java，各位帮帮忙；JDBC的3个jar导入了，在Eclipse中如果成功的话，就显示“连接成功”，否则连接失败。但是运行不了。
import java.sql.*;

public class testDBS{
public static void main(String[] args) {
String driverName = "com.microsoft.jdbc.sqlserver.SQLServerDriver";
String dbURL = "jdbc:microsoft:sqlserver://localhost:1433; DatabaseName=sample";
String userName = "sa";
String userPwd = "sa";
Connection dbConn =null;

try {
Class.forName(driverName);
dbConn = DriverManager.getConnection(dbURL, userName, userPwd);
System.out.println("连接成功!");
}
catch (Exception e)
{
System.out.println("数据库连接失败！");
e.printStackTrace();
}
}
}


下面是弹出的注释：
java.lang.ClassNotFoundException: com.microsoft.jdbc.sqlserver.SQLServerDriver
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at testDBS.main(testDBS.java:41)


帮帮忙解决下。谢谢了。