Software Ideas Modeler needs for its run installed .NET Framework 3.5.
Windows 7
If you have Windows 7, you needn't install anything. Windows 7 has preinstalled .NET Framework 3.5.1.
Windows Vista and older versions
If you use Windows Vista or one of previous versions, you must install .NET Framework 3.5. You can download it from Microsoft's site: .NET Framework 3.5 Setup
Linux
If you want to run Software Ideas Modeler under Linux, use the ZIP Package version in download section. Mono is required to be installed. You need also the package libmono-winforms2.0-cil. Software Ideas Modeler can be run using the command "mono /[PathToExecutableFile]/SoftwareIdeasModeler.exe".