Luckily, I have found my thread again...
This is a condensed instruction, I hope you can make use of it:
Copy your new renamed cfs3.exe (like cfs3vista.exe for example) from your CFS3 folder (example: C:\Program Files\Microsoft Games\Combat Flight Simulator 3) to your ETO folder (example: C:\Program Files\Microsoft Games\CFS3 ETO Expansion).
Then edit the MASTERETOSTARTUP.bat located from your ETO folder to this: Change the cfs3.exe to cfs3vista.exe
@ECHO OFF
CLS
CALL ETOEraSwapper.bat
CD "C:\Program Files\Microsoft Games\CFS3 ETO Expansion\global_layer"
CALL ETOGLSwapper.bat
START cfs3vista.exe
Save the .bat file. Click on the ETO start shortcut and you're good to go.
Please note: I had trouble saving the .bat file again. I even deselected the Read-only box but it didn't work. What I did is save it under a different name like, MASTERETOSTARTUP2.bat, and create another shortcut pointing this file instead. If you do this, remember to select "All files" (NOT a Text file) and ending the file name with the extension .bat.