Hawdware for Embedded Controllers?

the_arrow asks: "The company I work for is thinking about updating our control computer to something more modern. Does someone know of a good (and of course cheap) hardware with a small footprint, with at least two serial ports (one of them should be RS422) and an ethernet adapter? It must be able to run Linux. The other question is if we should buy Linux from someone (like Lineo) or try to make our own 'distribution' with our own drivers? The computers will be controlling both airport passenger boarding bridges and aircraft docking guidance systems (and maybe some of the other things we make)."