The authors present the results of low-temperature transport measurements on 'metallic' Si:Sb doping layers with nominal widths of 10 nm, 20 nm and 80 nm. There is clear evidence of weak localization and interaction corrections to the transport coefficients and for a 3D to 2D transition as the layer width decreases-the first observation of these effects in this system. Of particular interest is the fact that the experimental results are in good quantitative agreement with most aspects of the theory, despite the highly disordered and multi-sub-band nature of the samples.