You can use instructions here to get Ubuntu on a 1st gen ATV you can obviously skip the XBMC portion: http://wiki.xbmc.org/index.php?title=HOW-TO:Install_Ubuntu_and_XBMC_on_Apple_TV_1
The above instructions worked flawlessly on an old 1st gen I had laying around that I re-purposed. Once you have Ubuntu running you can use the standard 32bit Splunk installer. Considering the 1st gen ATV only has 256mb of RAM and and a 1Ghz Intel processor I hope you don't expect much performance. I believe there was a 40Gb and 160Gb hard drive model. If you have a 40Gb model space may become an issue.
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