Well I since I have no modding experience, how do I "grab the patch"? Sorry these questions may be so..."noobish" but work with me please.
The patch file for the feature you want. For instance, if you wanted
to turn grenades into mines then you would grab the
patch to the
Tremulous source code and compile.
If you were running Linux, then to apply a patch you might do this:
% svn co svn://svn.icculus.org/tremulous/trunk tremulous -r966
% cd tremulous
% wget www.example.com/path/to/file.patch
% patch -p0 < file.patch
% make
First line gets the source code, second gets you into the source code directory, third grabs the patch, fourth applies the patch, fifth compiles.
A good resource for various patches is the
Mercenaries Guild Patch Tracker which has all sorts of nice things.
The mod/QVM/whatever you like probably has a
list of patches that were included, and hopefully a link to where you can get the patches.
EDIT: I don't use Windows, but if you're running Windows you should be able to use
MinGW to do pretty much the same thing, in a similar (if not identical) manner. On OS X you should be able to do it natively (iTerm is in Applications -> Utilities -> Terminal).
Your stuff will be located in tremulous/build/ after the compilation.