MODDELING

Hello, I want to make my model request for GMod(http://forum.facepunch.com/showthread.php?t=1378745)I’m going to use L4D2 Human Riot Officers(http://www.garrysmod.org/downloads/?a=view&id=114924) but I want to replace their legs with Wesker’s legs(http://dl.dropboxusercontent.com/u/11830984/pictures/garrys%20mod/RE%201%20remake%20models.PNG)I also want to add a black visor motorcycle helmet but i can’t find one…So can someone explain me how to make all these things and tell me the programs i will need?For more info go here ====>http://forum.facepunch.com/showthread.php?t=1378745