I think you have some form of RTG with the Indivision ECS?
Indivision ECS provides modes like 800x600x16 colors, 1024x768x4 colors, HD720 x 4 colors, etc. I've used them all before on mine. With enough processor oomph the 800x600 mode can be pretty nice, but is hampered by ECS bus bandwidth. I've heard there's "RTG" drivers for the Indi, but from what I understand they're slower than things like SuperPlus.
Also - get a case for that darned ACA500! Can you imagine zapping that rare PPC board with static electricity from walking across your carpet and then brushing against it? The "Crystal" case is okay, but still a bad design not making it internal, IMHO.