3vil,
Firstly, make sure you have all the files for the mod in the EXACT same directories as they are set out in the other .pk3 files otherwise they wont work.
Then just add the mod to a .zip file and the rename the .zip with the .pk3 file extension! AND then you have your .pk3 file!
Finally, add the .pk3 file to the MOHAA/main folder (with all the other .pk3's), load up MOHAA and you SHOULD see your mod at work!
That ain't a very detail tutorial but it is a good guide!
Cheers!