the laptop might have vga or hdmi ports on it, but that is to OUTPUT video to an external monitor or tv. there is no way that i know of that you can input a signal to the laptops monitor.
yeah, you can hook it to a stand-alone monitor. you can do so by connecting via hdmi, if the monitor supports it, or you can buy a vga cable for the xbox and connect that way. im pretty sure the vga cable comes with an audio dongle so you can connect some pc speakers too, since vga doesnt pass sound.
Same goes for HDMI to DVI. It should work but you'll also need something else for sound. I've yet to try another output on my Xbox while using HDMI so I can only assume you can still use RCA/Optical outputs while using HDMI...