Coding/Script Programs?

[The chaser]

I could answer with a facepalm to that, but:

-Notepad++ will be enough for scripting.

-Here's the link for the level editor, model editor, material editor, etc
http://wiki.frictionalgames.com/hpl2/tools/start

If you want to make models, you can use Blender, Maya or 3DS Max.