Mac OS X Leopard pre-installed disk images for the 1st generation
Apple TV with the following modifications:

 * MenuMeters for monitoring RAM usage (256 MB is tight!)
 * Patches for working audio (except via HDMI)
 * Patches for the front panel LED

Download descriptions:
#1: Recommended 10.5.8 v2 for Apple TV with the following improvements
over v1:

 * Disabled Spotlight, Software Update, and iOS syncing to save RAM
   and improve performance
 * Fixed display of model identifier and memory speed in System
   Profiler/About This Mac
 * Removed unnecessary Hackintosh components

#2: 10.5.8 v1
#3: 10.5.5
#4: iDeneb-based 10.5.8 image of unknown origin

Restore the disk image to a GPT HFS+ formatted drive using Disk
Utility. If restoring to a USB drive, to enable booting, the partition
must be changed to appear as a recovery partition by setting its
partition type to 5265636F-7665-11AA-AA11-00306543ECAC.

For complete instructions, please see [this post on
TinkerDifferent][1].

Compatibility
Architecture: x86 (Intel:Mac)

Apple TV 1st generation (Model A1218)

  [1]: https://tinkerdifferent.com/threads/installing-mac-os-x-leopard-on-the-apple-tv-1st-generation.733/