Calculate Internal Rate of Return

We are building an investing website and would like to provide our users with the ability to compute the IRR for their investments. The formula and solution method are readily available on Wikipedia. We are looking for someone to provide us with the step by step solution. The solution must be either: 1) Detailed and simple enough that a programmer can code it 2) Even better coded for us already. Our website is a Joomla website and uses php, ajax, javascript etc... Ideally the formula should be able to handle multiple deposits and withdrawals at arbitrary time intervals.