Granted 32bit mode works on modern machines no problems. But going on the games Grey Alien is producing I suspect that quite a few target audience PC's will not be quite as modern as the FPS freaks have.
therefore, like I mentioned above:
I suggest you take a look at the highest supported resolution: if you see something low like 1024x768 as the maximum resolution, then the video card probably isn't very high end, and likely won't have a lot of memory to work with... you may want to consider defaulting to 16 bit at that point, so you save some meory you can use to store your images in. If you higher resolutions as well, you could pick the 32 bit version. Of course, after successfully launching the application, you can always make it customizable in your game options.