Here's what you do to set up CFS3 in Windows 7 for multiplayer. Nothing here should be any different to what Tailwind has already posted, but let me know if it is.
First install CFS3 on Windows 7. Just stick the CDs in the drive and let it get on with it. There's no special tricks even in 64-bit, the default options work just fine. You'll finish up with a CFS3 icon on your desktop. Fly the thing, then update to 3.1a via the two patches from Microsoft's CFS3 site and fly it again. You now have a vanilla CFS3.1a installation.
This is the 64-bit version of Windows 7 Home Premium. Find the CFS3 icon on your Desktop:-
You now have a copy of cfs3.exe named cfs3-Copy.exe. Rename this - I've called mine CFS3Online.exe:-
Create a shortcut to this renamed copy:-
The shortcut can now be configured for multiplayer via the shortcut's properties:-
There's one thing remaining, OLEACC.DLL. It's in your CFS3 folder and it must be deleted before multiplayer will work (don't shed any tears for this file, Win7 has its own version on the system):-
You're now ready to fly online using the CFS3Online shortcut. Watch your six, especially if Tailwind's around...