You might want to try adjusting the amount of video memory available to the virtual machine. It defaults to 256 MB and I would think you are better off giving that game at least 512 MB if not a Gigabyte of video RAM.
You can find information about how to adjust your virtual machine settings in the Parallels online help.
Keep in mind too that while many games work well with Parallels, not every game will work. Also keep in mind that games which demand a lot of hardware power, such as Saints Row 3 probably does may suffer performance-wise running with Parallels as a lot of computational power is required to run the virtual machine plus the software running within it.
Not to be negative or discourage you from trying this by the way. It might work to your satisfaction. Those are just issues to be aware of. For newer, demanding games going with bootcamp is often a better option for best performance and compatibility.
Lastly, it is kind of a long story but you never need to install any drivers in your Windows installed with Parallels. Parallels takes care of that for you. It is simulating a generic PC for Windows to run in and has its own drivers for that already setup.