If, like me, you have recently updated your development environment to Vista (x64 in my case), you may have noticed that double-clicking a .sln (solution) file with the intention of having it open in Visual Studio 2005 doesn't work, out of the box.
Well, not if you have User Account Control (UAC) enabled.
I just got around to googling this, finally, and found a solution which I shall repeat - in order to make it easier to find!
It works when you set both Launcher (C:\Program Files\Common Files\Microsoft Shared\MSEnv\VSLauncher.exe) and IDE (C:\Program Files\Microsoft Visual Studio 8\Common7\IDE\devenv.exe) to run as administrator. (Right click .exe and select Properties -> Compatibility, and choose Run as Administrator)
It should be noted that if you are running 64 bit Vista, you will need to look in C:\Program Files (x86), instead.