The basic information is here in this tutorial... http://freepages.misc.rootsweb.com/...rrainGeneration/Computer-generatedTerrain.htm
Follow the instructions carefully to install the HOG textures to make the tiger lines show up in Trainz. I think for TRS06 and above you save the textures to the desktop and have CMP commit them, but I'm not sure, since I work in 04.
If you're looking for the tiger data to make your own routes then the USGS Data Depot has the files. http://data.geocomm.com/
To know which Tiger files you need, go to the National Map Viewer. http://nmviewogc.cr.usgs.gov/viewer.htm
Both of these last two sites use pop-up graphics to feed the data rto you, so you have to turn off the pop-up blocker.