Creating a bootable ISO from a system HD?

So I've searched around a bit and ether is is actually really simple, or not..

If it is easy then:
I would basically just use disk utility to create a disk image of the HD and the use terminal to change it to an ISO. ??

I seem to have a similar situation to most with this.

I recently got a a new mac ( a mini) and I'd like to be able to run my old system(from my G4) as a virtual machine. Mostly because i want to be able to do backwards OS test runs, use the older programs i still have on that machine, etc.

I think my major detail question in this is would I be able to simply create an ISO of just the system itself so that I don't have some 20gig file of the whole HD?

Thank you

As far as I am aware, you can not legally virtualize OS X, not even on another Mac. There's been some controversy over this, however, and it does seem that Apple says you can virtualize the server version but only on a Mac running OS X server.

My take: Don't do it - it probably won't work anyway.

I guess getting an external terra-byte is in my near future then... Hopefully i can still run my older programs in 10.6