We present three-dimensional numerical simulations of turbulence in models of the ISM including the magnetic field, parameterized cooling and diffuse and stellar heating, self-gravity and rotation. We compare the physical-space density distribution with its representation in position-position-velocity space, noting that the two may give very different views, the latter introducing features of the velocity structure into that of the density. Finally, we present results of applying Principal Component Analysis (PCA) to the numerical data in order to obtain the velocity increment-size relationship and compare with the relationship obtained by Heyer & Brunt (1999).