weapons require a model, for which you can either use a preexisting model in the game (ie default gun and recolor it if you want), or you'll need to find/create a .dts model to use
to create models some common programs people use are milkshape, blender, and I think google sketchup, sketchup I think required some extra steps to export/convert it to a .dts
for the scripting behind weapons/server mods, notepad works fine
one of the best ways to figure out how to create what you want is to examine something similar to what you wish to create
to me, it seems that badspot created/included the default addons as examples for others to make mods off of
weapon scripts are somewhat simple, as you just copy a script for a different weapon and modify it
the server mod could be a bit more difficult because you haven't described what you're trying to do
