If you do a search there's a few threads with ideas on how to do it- from what i gather the thoughts are this:
1- you can't tell until it either lays an egg, or crows
2- you can tell and ways to tell are:
-as the comb starts- the boys have a 'bump' the girls down
-if you pull the first and third toe together under the middle toe and the aren't the same length it's a rooster (i think that's how it goes)
- shape of their head feathers
-you can't tell until it crows or lays an egg LOL
unfortunatly everone is telling me my runty pippa is most likely a Piper *sigh*