Tools and documentation can be found here:
http://wiki.frictionalgames.com/hpl2/

This includes tutorials and documentation for how to get started, basic scripting and other frequently asked questions.

If you have a problem, check the wiki and/or search the forum before posting a new thread. You are very likely to have a problem that has already been covered numerous times.

Helping us improving the wiki by adding articles, improving current articles or re-structuring it for better organization is very appreciated! All you need to do is to register an account at the wiki and you'll have full editing capabilities.