The comm API will silently "fail" to detect any ports if it cannot
load the native component. Are you sure javacomm.dll is on the library
path?

The installation is tricky and all of the parts have to be in the right
places.  Here is the little class I wrote to identify the serial ports
and also to tell me that the JavaComm API was installed correctly.  My
Windows XP installation requires the:

comm.jar file to be in the Program Files/Java/jdk1.5.0_03/jre/lib/ext
and the Program Files/Java/jre1.5.0_03/lib/ext directories.

javax.comm.properties file to be in the
Program Files/Java/jre1.5.0_03/jre/lib directory.

win32com.dll file to be in the Program Files/Java/jre1.5.0_03/bin directory.

import java.io.*;
import java.util.*;
import javax.comm.*;

public class Ports {
    public Ports() {
        CommPortIdentifier cpi = null;

        Enumeration e = CommPortIdentifier.getPortIdentifiers();

        while (e.hasMoreElements()) {
            try {
                cpi = (CommPortIdentifier) e.nextElement();
            } catch (NoSuchElementException n) {}
            System.out.println(cpi.getName());
        }
    }
    public static void main(String[] args) { new Ports(); }
}