Get the entire laptop, add an ethernet card if necessary, and install a fullscreen VNC viewer. Attach it to the computer you wish to display from with a crossover cable, install a VNC server on the main machine, and off you go! Booting the laptop off of flash memory might be faster too.
no use if the screen is not with a laptop
That is true.
If you boot into safe mode or some other trouble shooting mode you'll break it pretty quick. VNC can also be slow and buggy. Gaming (or similarly high demands on video) will be impossible. Plus any laptop that can manage the task well is going to be more expensive than a real LCD monitor. Prices keep falling and quality keeps getting better.