<applet code="AppletURLsx.class" width="60" height="100">
   <param name=target value="destra">
   <param name=etic0  value="Java">
   <param name=link0  value="http://www.valentinocondoluci.it/appunti/java">
   <param name=etic1  value="Html">
   <param name=link1  value="http://www.valcon.it/htmleco">
   <param name=etic2  value="IOI" >
   <param name=link2  value="http://www.valcon.it/ioi">
</applet>

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.net.*;

public class AppletURLsx extends    Applet
                         implements ActionListener
{
   String target_frame,
          l1, l2, l3, //link
          e1, e2, e3; //etichette
   URL    u1, u2, u3; //url 

   public void init()
   {
      target_frame=getParameter("target");

      l1=getParameter("link1"); e1=getParameter("etic1");
      l2=getParameter("link2"); e2=getParameter("etic2");
      l3=getParameter("link3"); e3=getParameter("etic3"); 

      try
      {
         u1=new URL(l1);
         u2=new URL(l2);
         u3=new URL(l3);
      }
      catch(MalformedURLException ex)
      {
         System.out.println("Problemi con i parametri?");
      }

      setLayout(new GridLayout(3, 1)); // verticale

      Button b1=new Button(e1); b1.addActionListener(this); add(b1);
      Button b2=new Button(e2); b2.addActionListener(this); add(b2);
      Button b3=new Button(e3); b3.addActionListener(this); add(b3);
   }

   public void actionPerformed(ActionEvent ae)
   {
      String nome=ae.getActionCommand(); 

           if(nome.equals(e1)) getAppletContext().showDocument(u1, target_frame);
      else if(nome.equals(e2)) getAppletContext().showDocument(u2, target_frame);
      else if(nome.equals(e3)) getAppletContext().showDocument(u3, target_frame);
      else                     System.out.println("Problemi con i pulsanti?");
   }
}

1. target_frame=getParameter("target");
   ...
   getAppletContext().showDocument(..., target_frame);

2. setLayout(new GridLayout(3, 1));