No issues in AOE. Only in Mozilla, and then only when I have too many windows/tabs open, especially ones with lots of graphics. Then, Mozilla suddenly can't refresh the screen, except whern you scroll or move the mouse over things. Other programs continue on just fine. If I swap windows from Moz to (e.g.) Opera, Opera shows up OK, but switching back, Moz can't paint the screen out over the previous Opera screen except if the page is long enough for me to scroll it down and then back up. I can see the tabs if I swipe the mouse cursor over them, switch between them OK, and (so long as the pages are long enough) scroll each one up and down to make it refresh.
Close enough Moz windows/tabs and the problem goes away. Open up too many windows/tabs and it comes back again.
Sometimes (but not always) I used to be able to make the problem go away just by closing other stuff, such as PMView or IE or whatever. (I.e., use less RAM.)
Windows 2000 SP4, Athlon, VIA chipset, never crashes (I mean never!, runs 24/7.