how to customize directories access


As everybody knows, it's worth separating directories like /var, /etc... in different filesystems ; above all, the swap should be in a special partition.
So i tried to do all that stuff on macos x ; i first make some symbolic links but i think i's better to mount directly the directories. How do i do this ?? (I tried the mount command but always a problem of partition type, and how to do this all the time at startup ?)

And How to have a swap partition instead of a swap file (located in /var/vm) !!