I'm not very good with linux but setting up a smoothie or ipcop is so simple even dave could figure it out without a manual. They have a simple 16bit colour GUI for installation, after everything is installed you can unplug the monitor, keyboard and mouse. Accessing all router functions are just the same as a normal router via a browser with a nice GUI.
I've only used smoothie and IPCOP so i can't comment on the others but i do lean towards IPCOP a little bit more as i find it's easier to find add-ons, and it also has a 'blue zone' for wireless.
If you do setup an IPCOP box make sure you install and setup the advanced QoS add-on, this way normal web browsing won't be affected by MJ-12.
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