  Positive magnetoresistance (PMR) of a silicon MOSFET in parallel magnetic
fields B has been measured at high electron densities n >> n_c where n_c is the
critical density of the metal-insulator transition (MIT). It turns out that the
normalized PMR curves, R(B)/R(0), merge together when the field is scaled
according to B/B_c(n) where B_c is the field in which electrons become fully
spin polarized. The values of B_c have been calculated from the simple equality
between the Zeeman splitting energy and the Fermi energy taking into account
the experimentally measured dependence of the spin susceptibility on the
electron density. This extends the range of validity of the scaling all the way
to a deeply metallic regime far away from MIT. The subsequent analysis of PMR
for low n >~ n_c demonstrated that the merging of the initial parts of curves
can bee achieved only with taking into account the temperature dependence of
B_c. It is also shown that the shape of the PMR curves at strong magnetic
fields is affected by a crossover from a purely two-dimensional (2D) electron
transport to a regime where out-of-plane carrier motion becomes important
(quasi-three-dimensional regime).
