As far as I remember it was done by a third party but used the Jet engine which enabled it to display animations which was its main use for me. The bad news is that I have been completely unable to get it to work in Windows 7 so have had to abandon it. The only disadvantage is that I can no longer view animations outside of Trainz which is a big nuisance.
FileViewer works reasonably OK in Windows 7 although the texture display in perspective view is a bit hit and miss (usually miss i.e. no textures) but it does what I want, which is to display attachment points or make measurements for adding attachment points.