I wasted a lot of time back in my first year at University playing the
orginal Command and Conquer in both the solo mission modes and against
buddies over the network. Electronic Arts has now made it available as
a free download. You can download both the NOD and GDI disks as ISO
images. I never did complete the game as NOD but did finish it as GDI.
http://www.commandandconquer.com/intel/default.aspx?id=61#NewsMain
Hat Tip: Ben Armstrong