The ideal way to find a program's installation path (on Windows) is to read it from the registry. Most installers will create a registry key for that program that contains the installation path. Exactly where this key is and what it will be named varies depending on the program in question.
To find if the program has a key in the registry, open 'regedit' and use the Edit > Find option to try and locate a key with the program name. If such a key exists, you can read it using the RegistryKey class in the .NET Framework library.
If the program does not have a registry key then another option is just to ask the user to locate the .exe file with the OpenFileDialog, although this is obviously not ideal.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…