When the i845 chipset was young, it came with driver support for 4:3 resolutions up to 1280x1024. By the time the current crop of widescreen LCD displays came around, the OEMs had lost interest in providing updates. The result is pretty much what you describe. The boxes I'm thinking of would be Optiplex GX260 vintage.
If you can/want to try, grab the last driver update straight from Intel. They did add support for things like 1440x900 later on.