Model hacking, what am I doing wrong?

I’ve been giving 3ds max a go lately, been trying to make some headhacks, followed tutorials, downloaded stuff. First I tried to do it the normal way by deleting the model’s head and placing the new on the body, it fucked up. Head went black and was all stretched. So I remembered the model actually had a full citizen face under it, so I just removed the cap. Fucked up even more, with parts of the body detached from the rest… At this point I supposed that either some of the software that I’m using is bugged, or I’m doing something wrong, but have no idea why. So, anyone who’s had some experience in modelling or hacking can give me some directions? Preferably for 3ds max as I’m pretty confortable with it, but I wouldn’t mind changing program too much if needed, I’m using a trial anyway

Some good directions is to not start with head hacks. learn how to compile normal models first.

Also 3ds max is a great program to model for source with. You shouldn’t worry about it being the problem.