  We use a semianalytical approach and a CDM cosmological model to study the
gravitational collapse and virialization, the structure, as well as the global
and statistical properties of isolated dark matter galactic halos which emerge
from primordial Gaussian fluctuations. From the statistical properties of the
density fluctuation field the possible mass aggregation histories (MAHs) are
generated, and these histories are used as the initial conditions of the
gravitational collapse. To calculate the structure of the virialized systems we
have generalized the secondary infall model. Although a range of halo
structures is obtained, the average density profiles agree with the profile
derived as a fitting formula to results of N-body cosmological simulations. The
comparison of the density profiles with the observational data is disscused,
and some possible solutions to the disagreement found in the inner regions are
discussed. The results of our approach, after considering the gravitational
dragging of the baryon matter that forms a central disk in centrifugal
equilibrium, show that the Tully-Fisher relation and its scatter can be
explained through the initial cosmological conditions. The sigma8=1 SCDM model
produces galaxies with high velocities when compared to observations, but when
the SCDM power spectrum is normalized to sigma8=0.57 an excellent agreement
with the observable TF relation is found, suggesting that this relation is the
natural extension to galactic scales of the observed galaxy distribution power
spectrum. The theoretical TF scatter is close to the measured one. The slope of
the TF relation is practically invariant with respect to the spin parameter
lambda.
