kaydash: When you're ready for modding the Quake III engine you'll already have enough experience to know when to start. The fact that you're asking for help is a clear and direct sign that you indeed to not have enough experience to successfully base a project around the engine.

I'd recommend working with C++ for another couple of months and get used to the language. Because I can honestly tell you that you're not ready to handle something on the scale of Q3, simply because its too much to digest at once. We're all just trying to save you some time here, because such a project is essentially destined for failure.

Keepin' it real.

Kaydash if you haven’t noticed these people are all giving you suggestions. This is that it has been proven that if you have little experience in the gaming industry and you try and do a large project you will get swamped and will almost always quit / fail. There are few who succeed but in the time it took them they could have easily learned the correct way to do it and have it only take 1/3 the time. I really suggest you listen and wait a bit on the Quake III source. I am unsure why you are so hasty at getting to it since nothing will come from you starting so fast except many turn a rounds, restarts and frustrating nights.

You didn't like my hypothesis? Ok i will repeat what everyone else has said. Get more experience first. If you're determined to work on the Q3 engine, get a very basic role in a mod so you can see how they use the engine without having to know much about it. But by simply setting a goal like "I must use the Q3 engine", the likelihood that you will not finish that project, and then get frustrated and leave game development forever, is very high.

I am the biggest proponent of FINISHING projects. If you look at my blog, I have been doing game dev for about 6 months, and I am still working on simple 2d games. Is it glamorous? No, but I know that in another 6 months I will have created quite a few projects, and have a good foundation in the future. Others who wanted to start by making the next World of Warcraft have absolutely nothing to show for it and will probably never mess with games again.

You choose your path.

"Humans have three ways to act intelligently;
first of all by thinking, that is the noblest,
secondly by copying, that is the easiest,
and thirdly by experience, that is the bitterest."

(Konfuzius)

If you want to take the third way, why don't you just start with setting up a project and try to compile the whole source and then start changing some values to see what happens.