I’ve just installed Debian Sarge on a HP Proliant DL320 without a hitch.
It is a Xeon 3.4GHz hyperthreaded with 1Gb ram and a single SATA disk.
I booted it via PXE since it has no optical drive and no floppy and ran the installation from there.
The basic system works perfectly, with a stock Debian 2.6.12 SMP kernel.
I still haven’t tried stuff like usb, rtc, admin interface etc. I’ve only had it for enough time to set it up to what its supposed to do 🙂