One of the challenges, with trying to establish pivot points on the 24 hour Forex markets, is that there is no standard market open and close, not until the weekend anyway.
For example, if your data source is from the UK, the day might start at midnight + 1 sec. Some Euro data feeds work off CET and US data feeds will quite often close the day @ 16.00 or 17.00 EST. Which time zone do you choose for the previous day's High, Low, Close? For this reason, pivot points become less reliable than they might be on markets, such as the Dax, Ftse, Dow, S&P etc., which have fixed trading hours.
Killphil08 has provided good links if you wish to incorporate PPs into your trading strategy. Imho, I wouldn't bother but, that's just personal preference.