Before I started using Macs, I used to take old, broken, Gateway laptops and turn them into little "Convertibles," as I like to call them. Well, I got a hand-me-down TiPowerBook with such a destroyed screen that I began using it as a portable 60GB FireWire drive. In the end, I couldn't help but make my first Mac Convertible.
The easy part was to image the machine using either Disk Utility or CCC, whichever you prefer (my image had 10.4.3).
When that is finished, boot it as a FireWire drive (if it hasn't been already) and boot another machine from it (preferably one with a monitor!). Set up an account with auto-login. Also, I think that if you hook up an external monitor at this point, then you *should* be able to set up display mirroring. I wasn't able to, because of a restriction I had with my booting machine.
If you don't have the luxury of setting it there, boot the TiPowerBook normally, with an external monitor attached. Wait for it to auto-login, and then put your mouse all the way in the top left-hand corner of the unseen screen (by default the external monitor is positioned to the right of the "primary" display). Click the mouse, hit the down arrow four times, and type mirror (this uses Spotlight searching, so it won't work on pre-Tiger OS), and then hit Return. This will bring the Secondary monitor display options on the screen -- and I believe there is a Gather Display Options button. Hit that, and it will bring you the other display screen. Feel free to set up the mirrored displays and -- ta-da -- you have a headless Tiger TiPowerBook.
I should note, in newer machines, just use the monitor switching function key... that makes this a lot easier!

