I'm also known as "Tycho" on StrategyCore forums. I've been studying disassembly and C++ coding since December of 2011. This all started because I wanted to mod the tank/cannon of '94 Enemy Unknown into a tank/chaingun for my own games. I started playing the DOS version but eventually switched to the CE version. At first, I focused on the sound problems which is when I started to experiment with Seb76's UFOloader.
If you're interested in the source code, it is available. Be warned you'll need to decompile the executable and be familiar with disassembly terminology to understand a lot of what the Extender does, since it inserts new lines into preexisting code. The source files for the Extender are here: File:UFOExtender-src.zip.
It adds a lot of functionality and fixes to the Collector's Edition (MS Windows version) of Terror from the Deep. Click on the title to get to the information page.
For those interested, here is the source code for the Extender.