My SMAC came in a box, but with no manual. Instead, the manual is on the CD. (I think companies are pricing games cheaper and no longer including those beautiful manuals like the ones that came with my Age of Empires, RR Tycoon2, Civ 2, etc.)
Instead, on the little download instruction booklet included, there is a statement on the back that says you can clip that off and send $5 and get the manual