Well, there are basically two separate problems here. a) Reading values from the serial port, and b) Displaying the values in the style of an old-school LCD digital display.
a) You can use the
Serial Library to get values from the COM port. You should get this working first (displaying the values via println() before you tackle the display part. It sounds like maybe you already have that working, but if not, that's your first step. The examples that come with processing include some serial examples, under Libraries / Serial I/O.
I would start with "Simple Read".
b) There are two ways to tackle the display. 1) With a font, or 2) by drawing the segments yourself (fun, but more tedious).
b1) The font method: Find a free font that resembles a digital display. Look at the existing typography examples to see how to use a custom font.
This tutorial is a good place to start. If you google "LCD Font" you'll find tons of free fonts that resemble LCD (liquid crystal display) characters, which is the style you are talking about.
b2) Draw them yourself. Big fun! You can draw the segments as polygons using beginShape(); vertex(); and endShape(); This will involve working out the coordinates of the segments (perhaps on graph paper) and storing them in an array. Then use another array (or the bits in an integer) to determine which segments are "on" for each character.
EDIT: Another intermediate method that occurs to me is to store each segment as a PNG (with transparent alpha) and overlay them on top of each other. This would enable you to draw the segments in a paint program or Photoshop.
