Hey, I was trying Crossover 8 and managed to get Command & Conquer 3 (demo version) working perfectly despite what has been on here (maybe the two demos fell in love, who knows). Anyway now for my fix. Sorry if this is the wrong place to put this :)
I'll make an excerpt from my blog to show what I did (My blog).
You'll need a copy of windows on a virtual machine or a friends computer. The game should also be installed on their computer, and then run once (with full setup etc, so a profile folder has been made).
Firstly, go to the windows computer/virtual machine that has Command & Conquer installed (and played/run at least once). Look in (forgive me if this is wrong):
c:\users\YOUR USER NAME\Application Data\Command & Conquer 3 Tiberium Wars\
This folder may be hidden or otherwise invisible, so you may have to manually type in the address in Explorer. Copy a profile folder (if the person is called "Shirley" in-game, their profile folder will have the same name).
Then after that you need to hunt down:
Main Partition/Users/YOUR USER NAME/Library/Application Support/CrossOver/Bottles/Name of the bottle which has CNC3 in it/drive_c/users/crossover/Application Data/Command & Conquer 3 Tiberium Wars/
For me that'd be:
Macintosh HD/Users/Christian/Library/Application Support/CrossOver/Bottles/Windows XP/drive_c/users/crossover/Application Data/Command & Conquer 3 Tiberium Wars/
Simply copy your profile into that folder by means of networking, USB, Floppy disk etc and you'll be able to fire up CNC3 in Skirmish mode in no time. And if for some reason that doesn't work or you are missing the CNC3 folder in Application Data, just copy the entire Command & Conquer 3 Tiberium Wars folder from the Windows PC's copy.