Anthony, have a look at the rental property simulator at http://www.peritus.iinet.net.au It is spreadsheet-based, cheap and displays all formulas so you can understand how it all works.
Hey Miccalady, have a look at this calculator (Rental property simulator): http://www.peritus.iinet.net.au It's spreadsheet based and displays all formulas for you. You really need not do anything apart from plug in your investment criteria.
I use a great little tool: Rental Property Simulator It is a spreadhseet-based tool, but kicks arse! and really cheap. They've been around for a while and they keep it up to date regularly (for free). Depending on which version you buy, you can analyse from one up to 3 properties at once. http://www.peritus.iinet.net.au/