After a number of false starts, we were about to give up on the Dell Optiplex 320 as a machine too weird to run Debian on. However, we persevered, and discovered the magic options that cause Debian Etch to not only install, but also boot.
pci=nomsi– this lets the installer (and, for that matter, the normal running kernel once you’ve finished installation) initialise the SATA disk controller correctly. If you omit this, you will see messages like “
Unexpected IRQ trap at vector c0“, and the kernel will refuse to detect any hard disks.