I suppose the next question would be:
Once you've compiled and built the code, which should result in a gamex86.dll and an idLib.lib file, what do you do with those files?
First off, idLib.lib isn't used by the game itself. You can ignore it for now. The only file you have to worry about inserting into the game is gamex86.dll.
Now, as to actually getting your newly built gamex86.dll into Doom3, I've seen three different opinions on the subject.
First, over at idDevNet (http://www.iddevnet.com/doom3/code.php
), they say you just have to put the DLL into the mod folder.
The other two come from threads I've seen here. Here are the links:
I'd think the best way to do it would be to follow the instructions from idDevNet, but I can't test it out until late tonight at the earliest. Perhaps someone else can post more details about handling the gamex86.dll file?