On my Riva128 card (4 MB), I selected to customize the X configuration. I tried testing 800x600 at 32bpp and 16bpp, both of them showed garbage on the screen momentarily and then returned immediately to the installer. Only 800x600/8bpp correctly showed the "Can you see this message" dialog. I use 800x600/32bpp on 6.2 with no problems.
I believe this is due to the same problem as in bug #12013
Not present in beta3.