A Windows machine. UnrealScript development is certainly possible on Linux, but you will be unable to access POSTed, which is a Windows-only tool. We recommend a Windows machine for development.
A copy of POSTAL 2 (duh)
An image editor or converter. Paint is an option, though a very basic one. You can probably get by without this, and simply use screenshots as your Workshop preview images, but an image editor will help.
For UnrealScript development, a good text editor. I recommend Notepad++[notepad-plus-plus.org]. There's even an UnrealScript highlighter[forums.epicgames.com] available, which will come in handy.
For UnrealScript development, the UnrealScript source code. This is included with the POSTed Development Kit tool in the local files (it's a zip file).
Creating a Development Environment
If you have not already downloaded the POSTed Development Kit, go ahead and do so. You will find it by going to your Steam Library, clicking on "All Games" and picking the "Tools" option.
Once the tool is downloaded, right-click on it, select "Properties", then "Local Files", then "Browse Local Files" to find the install location. Once you have done this, create a shortcut to the install location on your desktop, or in a place you can easily access for future reference.
Inside the install location you will find a zip file containing the UnrealScript source code. Extract the entire archive on top of your install location. This will create new folders called AIPack, AWEffects, AWGame, and so on.
Next, go into the System directory, and inside System create a shortcut to the command prompt, cmd.exe. Once you have done so, right-click on your new shortcut, hit "Properties", and delete the value for "Start in:". This will give you a handy command prompt shortcut that will start you directly in your System folder, which you can then use for launching ucc.exe for compiling scripts, as well as Postal2.exe for quick and easy testing.
Things We've Included For You
We've added a few goodies to POSTed's install to help you get started with development. Here are a few of them:
UnrealScript source, as noted above. You can find it in the base directory of POSTed.
UCC_Make.bat for quick recompiling of scripts. To use, simply delete the .U file you want to recompile, then run UCC_Make.bat.
TestMap, a simple weapons and NPC testing map with four rooms. One contains every weapon in the game. One contains nearly every NPC in the game. One contains a truckload of hapless bystanders for testing weapons in, and one is empty, to allow you to test without NPC interference. Feel free to make a copy of this map and put in your own weapons and NPC's to test.
A set of sample Workshop items in the WorkshopSample folder, available by unzipping the UnrealScript source. Here you can see the source code for several of my Steam Workshop items, plus a template mod for you to copy and adjust to fit your nefarious purposes.