Useful Links
Graphics Driver Updates
Nvidia - http://www.nvidia.com/Download/Scan.aspx?lang=en-us (Note: this site may require Intenet Explorer)
ATI - http://support.amd.com/us/gpudownload/Pages/index.aspx
(If you are not sure which ATI card you have, the automatic option is the top option on the right under the heading Automatically detect and install drivers) - Note: AVG Identity Protection may need to be temporarily turned off to use that tool)
Intel - http://www.intel.com/p/en_US/support/detect/graphics
If you are not sure what your graphics card is:
If you have TRS2006 or later, run TrainzDiag (<trainz install folder>/bin/TrainzDiag.exe) - it will tell you near the top.
If it's TRS2004 or earlier, right-click (My) Computer, then click Properties.
If you are using Windows Vista or 7, click Device Manager, if using XP, click Hardware, then Device Manager.
Click the + next to Display (Adapters)- the name that appears here is your graphics card.
Other Useful Links
Trainz mainstream service packs: http://www.auran.com/servicepacks/
This does not include regional variations like Steam, Just Trains etc.