There are still not that many device drivers available for AtheOS. But since the kernel can call BIOS function it can still work on a lot of hardware (at the cost of performance of course). The worst area is network and video. It is possible to boot AtheOS on a "unsupported" graphics card if the card supports Vesa 2.0. It will run but the GUI will of course be dog slow!
Here is a list of supported hardware:
CPU: Pentium or better (Yes AtheOS use Pentium only instructions and will crash and burn on a 486). Chipset I have tested AtheOS on a few machines, and it seems to run well on those. I know other have had problems getting AtheOS to run on various machines but it is uncertain whether this is caused by the chipset. Video adapters
Mouse: Most PS2 and serial mouses should work. It used to be a problem with logitech serial mouses but that seems to be solved now. Network:
Disk There is an IDE driver on it's way (only tested on one machine, and not part of the current distro). But generally all disk accesses are done through the BIOS, so most IDE and SCSSI disks should work. I even boot AtheOS from my panic ZIP disk every now and then.
You can also find a list of machines that AtheOS has been successfully installed at here