The quality of that monitor will be as good as it can be if you connect it to a port replicator. YOu'll be fine on that end, but if the monitor's not as bright as your LCD and if it doesn't support the same resolution, there's no helping that.
I have had my IBM T42 for about 7months. For the next 4 to 6months, I won't need a laptop. My notebook only has a 14" display and the screen resolution is 1400x1200. If I buy the ThinkPad Port Replicator II and connect a 19" Dell LCD display to the T42, will the picture quality look good? Do you need a special graphics card to get the best picture quality out of a 19" LCD display?