Simple answer should be yes, you should
be able to boot onto the 250Gb HDD, in order to install steam onto the 256Gb SSD.
That being said, be prepared to use a USB stick, or DVD.
I can't say for sure if you would need to boot into DOS in order to install from the HDD.http://www.steamcommunity.com/groups/steamuniversehttps://github.com/ValveSoftware/SteamOS
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