Let me start for apologizing for my bad grammar. English is not my first language.
So here is what I want to do.
I need to build my own Linux distribution for a class in college. It's a contracted work for more points and I have limited resources.
I cannot afford to buy a 'dummy' machine so I thought I could use Vmware Fusion on a Mac. I can build just fine. But somehow my work goes away if I restart the Vmware machine. I'm assuming because it's booting from the ISO file each time.
My question is how can I, or even if it's possible, to tell Vmware to use an external hard drive for this project. Kinda how it can boot to the bootcamp partition. I want it to be able to boot to an external hard drive.
You should check out Linux from Scratch in VMWare it's written for VMWare Workstation but it will work almost the same for Fusion. Its a complete guide to setting up a LFS Build environment in VMWare
You're using a linux live CD? Don't do that if you want to persist settings. Pick a distribution, create a new virtual machine & do a proper install.
For the virtual machine tell VMWare to use a vmdk virtual hard drive from the external hard drive. This should then just boot as normal; just remember to make sure the external drive is plugged in before trying to start the VM :-)
This will allow you to try installing your distro into the virtual machine over and over and over again as much as you like :-)
Hope this helps.
EDIT: good points in the comments concerning snapshots, if you are not just putting some packages together you'd be better off installing to a virtual hard disk - this guide is for Ubuntu