I'll hunt down my old G4 CD's and try to install. I'll report back in a few minutes
Edit: All 4 CD's installed properly and I should note that i did nothing more than insert the first CD and let it autorun, at which time i selected the setup button however the DirectX 9C that comes with the Realflight G4 did not install as it is not compatible with the Operating system. This shouldn't be a problem for me as I have 6.5 and 7.5 currently installed and they work with the same required DirectX files but may be an issue for other people. It is currently updating to 4.5
Edit #2: I am flying the Extra 300 on a fresh install of RealFlight G4 in Windows 8.1. No issues after the update to 4.5.050.
System: Windows 8.1 Pro with Media Center 64-bit (6.3, Build 9600) (9600.winblue_r7.150109-2022)
Processor: AMD Phenom(tm) II X6 1100T Processor (6 CPUs), ~4.2GHz
Memory: 8192MB RAM
DX Version: DirectX 11
Installed in: D:\Realflight G4
Free Disk Space (D:\): 378384 mb free
Launcher Version: 1.00.041
LauncherHelper Version: 1.00.326
RealFlight G4: 4.50.050
It is possible your CD's could be damaged if that is the case you can
Contact Technical support and see if they can replace them or for
$50.00 and your existing Interlink Elite, you can upgrade to 7.5