Anisotropic Type I string compactification, winding modes and large extra dimensions

We discuss the structure of general Anisotropic Compactification in Type I D=4, N=1 string theory. It is emphasized that, in this context, a possible interpretation of M_{Planck} as ``dual'' to (at least) one of the Kaluza-Klein or Windings Modes could provide interesting interpretations of the ``physical scales'' and the GUT coupling. Some of the scenarios presented here are strictly connected with the phenomenological proposal of TeV-scale gravity (i.e. millimiter compactification). We show that in this scenario new and probably dominant effects should arise from the presence of ``low-energy'' Winding Modes of usual SM particles. Stringent bounds on the Planck mass in 4+n dimensions are derived from the existing experimental limits on massive replicas of SM gauge bosons. Non-observation of Winding Modes at the planned accelerators could provide stronger bounds on the 4+n dimensional Planck mass than those from graviton emission into the bulk. Some comments on other possible phenomenological interesting scenarios are addressed.