My comparator class
----------------
private static class ComparatorImpl implements Comparator {
    // the o1.equals(o2) prevents the "a" "a" problem Ryan pointed out
    public int compare(Object o1, Object o2) {
        return o1.equals(o2) ? 0 : -1;
    }		
}
----------------
My map thingy
---------------
// comparator is a static shared instance of ComparatorImpl above ^
Map map = new TreeMap(comparator) {
	public String toString() {
                // ends with 'd' and 'e' per BEncoding way
		StringBuffer buffer = new StringBuffer("d");
		synchronized (buffer) {
			Iterator iterator = keySet().iterator();
			while (iterator.hasNext()) {
				String key = (String) iterator.next();
				Object value = get(key);
				buffer.append(key.length() + ":" + key);
				if (value instanceof String) {
					String string = (String) value;
					buffer.append(string.length() + ":" + string);
				} else if (value instanceof Long) {
					buffer.append("i" + value + "e");
				} else if (value instanceof List
						|| value instanceof Map) {
					buffer.append(value.toString());
				}
			}
			buffer.append("e");
		}
		return buffer.toString();
	}
};
--------------------
My test method (well, not really)
-------------------
public void testOrderedMap() {
	Map map = BDecode.decode("de");
	map.put("length", "19267903");
	map.put("path", "stage1-x86-2006.0.tar.bz2");
	java.util.Iterator iterator = map.entrySet().iterator();
	while (iterator.hasNext()) {
		java.util.Map.Entry e = (Map.Entry) iterator.next();
		System.out.println(e);
	}
	System.out.println(map);
}
--------------------
output is...
path=stage1-x86-2006.0.tar.bz2
length=19267903
d4:path25:stage1-x86-2006.0.tar.bz26:length8:19267903e

which is okay, except toString at the bottom should be

d6:length8:192679034:path25:stage1-x86-2006.0.tar.bz2e

Since 'length' key-value pair was placed BEFORE 'path' was.