The OS/2 Museum has made available the first version of a display driver disk for Windows 9x running on VirtualBox. The driver uses a linear framebuffer and supports 8/16/24/32bpp modes with resolutions up to 1920×1200 pixels. The driver is not accelerated but tends to be very speedy on modern hardware.
I cannot wait to try this out. The linked article also includes a few notes about the development of the driver in question – it won’t come as a surprise that this wasn’t an easy process.