Archive.org has archived a site with the tools required for modding O.R.B. Unfortunately, I am unable to find the tool the developers released for Res files, so you will be unable to pack the files you extract back into them, however, O.R.B can be made to read the ini(dbf files are read from them by default I think, if not simply alter orb.ini to correct this) files from the directories directly by altering settings in orb.ini in the game directory. edit mod_enabled to be 1, alter flag_read_as_ini to 1 also. There were some other flags to modify(I think game mode had to be 3?).

Unfortunately I have been unable to find archived versions of the O.R.B forums, where a developer released the tool they used to make the .res files. He also revealed several pieces of information pertaining to modding O.R.B(which I have since forgotten).

https://web.archive.org/web/20100212203731/http://www.b5mods.com/tools_orb.htm

You will find a lot of content that was planned for the game that never made in, such as a Aldar Dreadnaught, Kuy'lek starbase(yup yup, but it lacks the required model hardpoints to function as one among other things). There are even some voice recording for the campaign that seem to be from a older version of the story.

Theres some sort of flags for editing the tech tree in orb.ini, but how to access that feature remains shrouded in mystery. A file called default.rst contains the research tree entries, but how to add new ones doesn't seem entirely straight forward via hex editor, at least on a quick look I can't seem to find easy commonalities between the entries.

[edit]since I happen to own the CD version also, I extracted the original default.rst from it so it can be used to detect the changes between the 1.4 version, and release(given the patches added new ships to the Malus and the Alyssians). If somebody more experienced in hex editing can provide insight, it would be great, cause it is unlikely I will find a way to add new research items via hex editing quickly.

http://www68.zippyshare.com/v/26809846/file.html

[edit2]hmm, seems somewhat suspect if that ini loading flag works, at least I can't seem to make the game load my modified default.rst that way(and the copy I place in the main folder gets replaced by a odd 1kb file with no entries in it, then later with a copy of the file from the .res file). Might have been wrong about what that flag does, so presumably you would need to make a tool that can pack .res files so you can alter the research items in the game.

[edit3]for those interested, at least the debug output seems to work

stuffout_on=1
debugout_on=1
trace_on=1

and all produce a txt file with debug output, them being stuff.txt, debug.txt, and trace.txt in the main game folder.

[edit4]ah yes, finally found the instructions for activating the tech tree editor, a developer called Black Box revealed this information in the O.R.B forums originally Now, you can ignore the bit about editing orb.ini & extracting files from dbf.res in the above quote. However there is one line in orb.ini that you must edit, develop_tree, change it to 1.

The shortcut with that command will start the scenario editor. Simply go to Layer, then Player 1 Properties, and click the Research Node button. You have now opened the tech tree editor. Clicking new near the bottom will start a new entry, which you then have to select after you have created it then specify its properties. Look at the existing tech tree entries to figure out the groups and such.

Depending on which race you have selected under race properties will define which tech tree you are editing.

The game will save the edited default.rst into the games main folder. However, I do not see the game utilizing it, so I dunno if there is another line in the settings file you must edit to make it use it, or if you have to pack it into ini.res in the orbdata/races folder(which would require a tool capable of compiling .res files).

[edit5]btw, Fileplanet does have a mod that changes a ton of things in the game http://www.fileplanet.com/186075/180000/fileinfo/ORB---Planetary-Mod

I've finally found the file required for compiling(and extracting from) the .res files made by the developers of O-R-B.
I found a thread in archive.org copy of the original O-R-B forums(after it occurred to me that the site might have some user profiles stored, which would allow me to find the posts with them, and I did). The link contained in the thread I found still works, and I've tested that the program works.

http://www.isomedia.com/homes/nickerso/ORB/big_file.exe

and here are the usage instructions [edit1]by editing the .dbf that defines the Malus ships, and adding a research item that unlocks the Malus Mine-layer, I've successfully managed to make them buildable in game. However, each scenario that comes with the game must be resaved for the changed tech tree to take effect, each scenario keeps its own copy of the tech tree with it. The Mine-Layer is fully functional, you give it a move order to a destination, then give the lay mines order, and the Mine-Layer will lay mines at the destination. I've not yet tested if the mines work on enemy ships(game just crashes when I get one Mine-layer within range of a enemy vessel every time...)

I've also confirmed some limitations. Malus or Alyssian research items cannot unlock items outside of their species. If you want to make the Aldar/Malus Hybrid ships buildable, you must make clones of them for the Malus for that to be doable. I've looked into the executable, and confirmed that you also cannot give the other 3 species tech trees, the game simply does not have the code for handling that, it only has code for handling Malus, and Alyssian tech trees.