Nanoforms of silicon such as nanoparticles and nanowires have been attracting much attention and recent findings of novel metal encapsulated silicon clusters as well as nanotubes have opened up new avenues for the development of silicon nanostructures. We review these recent developments and discuss the findings of the metal encapsulated nanotubes of silicon and germanium using ab initio total energy calculations. These nanotubes are generally found to be metallic. The metalicity is not induced by the doping of metal atoms, though they stabilize silicon and germanium in tubular forms. Transition metal atoms such as Mn and Fe lead to nanotubes that are ferromagnetic making them interesting as nanomagnets. Antiferromagnetic and ferrimagnetic phases have also been obtained. A novel aspect of these magnetic nanotubes is the possibility of developing half-metallic nanotubes that could be interesting for nano-spintronics applications. Further possibilities of semiconducting silicon nanotubes are discussed.