Is it possible to use a laptop as the usb mon/kybd on a mini lunux pc
(eg minix, raspberry pi..)?

On the BeagleBoard systems, the board "publishes" an RNDIS network
interface widget, and runs a DHCP server on it. So, if you plug the
board into your laptop via a USB cable, the your laptop "sees" another
network interface appear (complete with IP-address service).

You can then run any sort of terminal emulator you want on your
laptop, and access the BeagleBoard via a "ssh" network session.