I got an old Compaq Armada 7400, and decided to install Linux on it. I tried Slackware, but I decided to go with Gentoo.
This guy has one like mine, and he put Red Hat 9 on it. He has some useful dmesg and lspci listings posted, which I won't bother to duplicate.
Here is the Armada 7400 Service Manual. Unfortunately, it's broken into PDFs by chapter, rather than a nice, single file.
I tried a few versions of the gentoo-sources 2.4 kernel, but I never really succeeded at getting everything working quite right. I had considerably more luck with 2.6.1.
I also added a 3Com 3c589 PCMCIA network adapter.
To get everything configured, I selected the drivers for the hardware above. I disabled ACPI altogether, and enabled APM. I selected to use APM to blank the screen. I enabled the console framebuffer, using the VESA driver. I enabled PCMCIA support, using the Yenta driver.
That was pretty much all there was to it. One thing that had worried me a bit was the cooling fan, which starts up only when the system begins to get warm. While running Slackware, I had some problems with the fan never starting, and I was a bit afraid that when I started doing hours-long kernel compiles on this slower computer, that the system might overheat. It appears that with a properly configured kernel, specifically, ACPI off and APM on, the fan works just as expected, though I haven't been able to use lm-sensors or similar to get the status of the fan or sensor.