Steam users will get this update automatically and it will take you to build 94812 (PC) or 95086 (Mac).
This update includes;
Raildriver support
Multiplayer updates
AI updates
Over 100 additional fixes and optimisations.
For assistance with Raildriver calibration click here: http://online.ts2009.com/mediaWiki/index.php/Raildriver
Full report here: http://www.trainzportal.com/news/view/tane-sp3-officially-released