Linux can be run either purely from a command line (similar ms-dos's window) and if you run it in this mode, you can run linux on pretty much ANYTHING... However if you would like a GUI (Graphical User Interface) it helps to have about 128mb ram and at least a onboard video card. My server runs fine with 128mb ram and a 8mb savage 3d card from back in the day
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Linux has a bunch of nice themes for the GUI Desktop inferface and it is HIGHLY customizable
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look at
http://kde-look.org i think