harder

Is it possible to make the parts of the enemy character model below the neck invisible, apart from the gun?
so all you see is a game full of floating heads and guns?(I'm thinking maybe a texture hack?) so that all I have to aim at is the head

yeah of course
you can put color on it
just try to delete that part
( I think )

It is possible to make textures invisible, though its pretty much recommended that you dont bother, especially when it comes to actual player models, as there is a lot of files to convert.