Screens either come with a VGA port, an RCA port, or both. It really depends on the resolution (and cost) of the unit. One with just an RCA port will display at TV quality, which generally gives up to 800X600 with a computer attached before the image becomes unreadable.
You could get a VGA to RCA adapter and be able to plug in the PC, but you will have to use lower resolutions. Remember, the inputs are generally geared towards the resolution the unit can display. A unit with an RCA input won't have nearly the pixel density of one with a VGA port.