Can he still see the text 'normally' (that is, can he still read things, even though they might be slanted/skewed).
Try lowering the resolution to default values (say 800*600) just to be safe, and then start configuring the monitor itself, changing the horizontal and vertical components using the on-screen display (OSD), there are buttons on the monitor so you'll be able to work it out.
If it's on "maximum stretchness", filling the entire monitor screen, then that's something I've never seen before. I *had* a proview in 1999 (15" CRT), and it failed on me. The monitor "died" -- stopped working, but before it did I would get random jerkiness, bits of the screen "chopped off" (some parts visible, some parts black), and overall unreliability.
I think he should buy a new monitor, because it's too old to keep, and it would cost a bit to replace (if there is any hardware fault).
Try plugging in another monitor, or have you tried using a different video card? Lowering the resolution? Changing the bit depth? Updated any video card drivers lately?