Bah I need to nwo it kills me

Any text editor will probably work. I use the shareware Tex-Edit Plus, because that's my favorite text editor, and I've used it for the better part of a decade now.

To get started, do a lot of copying and pasting. If you want to modify, say, the M-16, copy the m16.gun file, rename and open your copy, then futz around with what you want to change. To add your new weapon to the game, you have two alternatives: first, if you wish to replace the original M-16, you can simply rename the original m16.gun to m16.gun.bak (files with the .bak suffix are not read by the game) and your version to m16.gun. Then the M-16 in the game will be your version. To ADD your gun to the game rather than replacing another gun, it requires a little more work. Call the .gun file whatever you want. Then you will need to make a kit for it. The easiest way of doing this is to find a kit which has the items you want (nades, sensors, etc.) and copy its file. Rename it whatever you want (mygunsensors.kit or the like works just fine), and then open it and change the weapon name to point to your new .gun file. Then, back up and open origmiss/Kits/no_restrictions.kil and add the filename of the kit you just created to the platoons. If it's a rifleman kit, add it to the end of the four rifleman entries. If it's a demo kit, add it to the end of the four demo entries, etc. Then, you can start the game and select your new kit.
To get the name of your gun working correctly (after following the preceding instructions, your gun will show up in the game with a name something like "!key"), you'll need to add an entry to the GhR/GhR Data/Shell/strings.txt file. Back it up, then open it and add a line with a key and a name. The key will be something like WPN_M4 (it does not have to follow that exact format), and the name will be something like "M4". Once you've entered that, open your .gun file again and on one of the first lines, you'll see something like "<NameToken>WPN_MG3</NameToken>". Change the nametoken to match the key you just added to the strings.txt file, and now your gun should be named correctly in the game.

If you're going to play around with modding, you can change the origmiss and mp1 files easily, but be sure to change them back when you're done. The best (safest) way to play around with modifying guns and kits is to create your own mod. All you need to do is create a folder in the GhR/GhR Data/Mods folder, then copy a modscont.txt file from another mod, and change the name inside the file. The name entry in the modscont file is what will show up in GhR when you go to the "Mods" pane of the preferences.
The folder hierarchy for a basic weapons and kits mod is as follows:
GhR
|-----GhR Data
| |-----Mods
| | |-----Your Mod's Folder
| | | |-----Equip (this is where all the .gun files go)
| | | |-----Kits (this is where the .kil kit restriction files and the .kit files go)
| | | |-----Shell (this is where your own strings.txt file goes)

The hierarchy above will allow you to create new guns and modify existing ones, create and modify kits and kit restrictions, and name your guns what you want or change the names of existing guns. To add new models and/or new sounds, you will need more folders in your mod's folder: Sound (for sounds, duh) and Model and Textures if you wish to add new gun models. Adding new sounds is relatively trivial, and I'll explain it if anybody wants. Adding new gun models is equally easy, but creating your own requires a PC.