Trainz/API and Scripting Guide

Trainzdev and the Trainzdev wiki has much more current information for later versions.

TRS2006 Scripting and API guide http://web.archive.org/web/20060310072511/http://files.auran.com/TRS2006/manuals/TRS2006-API.zip

TRS2004 Scripting and API guide (Local drive)/Auran/TRS2004/Scripts/docs/index.cfm

Also see the scripting section in the level above.