Slew of LiveCD / USB questions, dunno where to begin

[SoulinEther]

So I figure there's no way I can google this without knowing some specific knowledge in advance, and since I'm not sure where to turn, I turn to you, my fellow café-goers.

I want to turn a portable hard drive into an Ubuntu LiveCD. That isn't not doable, i think I might even know where to look for that, but.. that's not where I'm stumped.

So I bought this USB hard drive. It seems bootable. So that helps. But here's the thing: the laptop I want to use it with cannot boot off of USB. I don't want to install Ubuntu on the hard drive (the laptop isn't mine), plus I want to be able to carry it from computer to computer. And... i would like to be able to boot off of both the hard drive ... or a CD.

Which segues into my next question: How do I boot off of a CD and tell it to load the LiveCD or the squashfs or whatever on the hard drive?

Can this hard drive retain data? Just by simply auto-mounting another partition on the drive to /home?

Can the squashfs be modified mid-use and be re-written?

Has anybody else done this and has it been successful?

Is the cafe where I want to post this? Hm, i think, since it's not mission-critical that I find out how; it's more of a hobby than a need.

Thanks.