Convert a php application to an .exe that will run on desktops

We have a developed web based php application (comprised of php files and images) that calculates how much storage space is needed based on how many rooms you specify. You can see the application here: [login to view URL] What we need is to have this application converted to an .exe that runs on a personal computer. Mostly we are interested in it running on all windows computers, but if it is not too expensive to have it built for macs we might be interested in that too. Apparently building an .exe that runs on all windows platforms is not particularly easy unless you install it as part of install shield or something similar (so that the right dll versions are used), so this would be our expectation of how this project is delivered. We would expect this could be done in either VB or C but we do not have a strong preference on language. The finished product must run standalone with no need to install an additional environment (such as an IDE). The user would go to a website URL to download and install the application.