For starters it does work for Vista and Windows 7, as well as in virtual machines too. If your having an error on open then your missing some .net files. This application uses .net 3.5, and you also need the Microsoft Visual C++ 2010 Redistributable Package if your getting errors. As far as XP, that's a decade old operating system almost completely unsupported nowadays, but as long as you have all the required dependencies (which are NOT included in versions older than Vista), then it should work.
As far as people having the problems with the application.... Please download the new version, and please read the bold print at the bottom of the release page. This application requires the ps3keys be in the right folder because they are used with unself. The program now err checks better (I accidentally buried the elf creation detection inside of another if statement), and some other various minor upgrades and improvements. The newest version is available
here.