If Crossover fails to detect your video memory amount, Sims 3 will use whatever Crossover guesses which is likely 128MB.
Since Sims3 configures it's default options based on available video RAM this can be very important.
The solution is to place your video memory amount into the registry at:
HKEY_CURRENT_USER: Software: Wine: Direct3D: VideoMemorySize
This generally works for all games that query D3D for the GPU memory size.
This will determine the maximum amount of memory that WineD3D will advertise for games to use. This is a soft limit, the handling of which is determined by games and your video driver, not WineD3D.
The Sims 3 in particular cannot detect over roughly 2GB of video memory. It's probably best to set this to 2GB of video memory even if you have more. On modern video cards the game is more likely to run into game engine design limitations than video memory limitations.
You can also set your PCI Vendor ID and PCI Device ID here if they are not being detected properly. While you can "lie" to games about this. It is not recommended as most games tune their feature set for the cards they are using.
