[CentOS] Flaky graphics - need help nailing down the cause

This morning I noticed that my (new in July) monitor was behaving
strangely.  At first, it was odd parts of web page graphics that
didn't show up unless I scrolled up and down in the window, and then
they weren't displayed with any consistency.

Then I noticed that the screensaver failed to appear (computer was
locked, but graphics never showed on the monitor).  I tried running
mplayer to play a movie I have on the system, and the window remained
black (sound was fine).

When I move a window, parts of it (pixels scattered across the window)
don't refresh during the move OR even when it is done, unless I run
the mouse over them or, in the case of the menu bar, click on one of
the options.  The nautilus window that sometimes comes up after a
reboot was not fully painted with the text parts of the entries below
the mouse cursor on the screen until I ran the mouse over them, and
then only the ones I "touched" refreshed properly.

During the system shutdown and restart, the text is scrambled beyond
recognition, although the graphics during the boot, driver init and
login screen are fine.  Most of the screen after I log in shows up,
unless the default terminal and nautilus windows show up, and then
they're not all there (as above).

DVI-VGA: same problem either way
2.6.18-92.1.10 - 92.1.13: likewise (makes no difference)

The video card is an nvidia ge7100gs and I have the beta driver from
rpmforge (under dkms).  The base system is an ECS nFORCE4M-A with an
AMD Athlon 64x2 and 4GB of OCZ main memory.  The newest parts are the
main memory (upgraded from 2GB about two months ago) and the monitor
(new in July).  The m/b, COU and graphics card are all about 18 months
old.  I recently upgraded to the new 92.1.13 kernel.

Question:  Is this the monitor (most likely), the video card, the OS
or the base system, or something else I have not considered?  Is there
a good video test program I can use to diagnose this properly?

I have a two-year replacement warranty on the monitor, so I will use
it if I need to, and I think it's still under the manufacturer's
warranty anyway.

Thanks.

mhr