Whenever something updates the screen, I see little dots flashing randomly nearby -- for example, when something is animating in a dialog box then I see lots of little pixels (of random colour) pop up typically to the right of the dialog.

They're not permanent -- they just flash up for a fraction of a second and then disappear. But it's highly annoying.

It's doesn't seem to be the display manager's fault; a fresh install of X running just TWM still has the problem (though it's more noticeable in KDE or Gnome because they update the screen more). And it happens in both XFree86 and Xorg.

The video card is a Diamond Stealth 3D 2000; I'm not sure exactly how much RAM it has.

Some excerpts from my config (this is all pretty much autoconfigured, except for the "fifo_conservative", which I added because it seemed to help a little:

Section "Module"
Load "GLcore"
Load "bitmap"
Load "dbe"
Load "ddc"
Load "dri"
Load "extmod"
Load "freetype"
Load "glx"
Load "int10"
Load "pex5"
Load "record"
Load "speedo"
Load "type1"
Load "vbe"
Load "xie"
EndSection

Section "Device"
Identifier "Diamond Stealth 3D 2000"
Driver "s3virge"
Option "fifo_conservative"
EndSection

Section "Screen"
Identifier "Default Screen"
Device "Diamond Stealth 3D 2000"
Monitor "Generic Monitor"
DefaultDepth 24
SubSection "Display"
Depth 24
Modes "1280x1024" "1024x768" "800x600" "640x480"
EndSubSection
EndSection

Any ideas how to fix this?

First up, Welcome to LQ

Second of all, a quick LQ Search yielded this thread which may fix your problem.

It seems that this particular card doesn't like 24bit colour. Try dropping it down to 16bit and see if that fixes your problem.

Baldrick

Cool! That did indeed work. I didn't even think of that one, since 24bit colour works fine under Windows. Weird. Still, thanks for the quick response!