We have shown that a semiconducting single-wall carbon nanotube (SWNT) can be covered uniformly by titanium atoms and form a complex but regular atomic structure. The circular cross section changes to a squarelike form, and the system becomes metallic with high state density at the Fermi level and with high quantum ballistic conductance. Metallicity is induced not only by the metal-metal coupling, but also by the band-gap closing of SWNT's at the corners of the square. Even more interesting is that uniform titanium-covered tubes have magnetic ground state with significant net magnetic moment. Our results have been obtained by the first-principles pseudopotential plane-wave calculations within the density-functional theory.