the several mods are downloadable on this site.
However the programs that u need to mod yourself are not always easy to obtain.
However if you search some old threads you will find plenty of links that will lead to the desired program.
Programs u might need:
Vachu's bar explorer ( search google )
Cheesy's animation editor ( search google or go to his site )
Gmax ( there is a link in an old thread )
Aommed ( downloadable from this site )
Rescourcehacker ( downloadable from this site )
Also it could be useful to read the guides that for example Auron made about modding, so you know what you are doing, because modding involves lots of work, its not something you on a free afternoon.
Noobs do not excist.
There are just players and better players.