When calculating internal rate of return you can use the provided calculator on your series of cash flows. The IRR formula is built into the calculator.Free 30 Day Trial of MarketWatchs' Hulbert Interactive Newsletter
You will see two series of cash flows. Each series of cash flows support the IRR result at the bottom. To obtain a IRR for your cash flows, you need to supply the actual cash flows from your project. Be sure to clear out the numbers to zero for the years not needed. The year column can be changed by just changing the first year.
Once you have finished calculating internal rate of return for each of your projects, you can make a rational decision about which project is most economical for your situation. Warning! The IRR found may not be valid if the cash flows swing back and forth from positive to negative values. It is possible to have more than one IRR answer in that case.