I have the same setup as you; a Shuttle S20G5 with a SATA hard drive. I was able to get Debian installed but when it reboots I get a kernel panic after I choose Linux in GRUB.
I used one of the daily builds for the debian installer. I used the one dated 20050721 because I was having trouble with the more current one (20050729). I started the installer using 'expert26' mode. I got to the point where it asked my what disk module to load, I choose the 'sata_uli' module. The installer will say it didn't detect any disks but if you just select 'Go Back' and then select the next step (I think its like detect hardware or something), it will allow you to go forward. In the detect partition step, it will see your SATA hard drive and you can continue with the installer. I think this 'workaround' was fixed in the current debian installer build. I was able to install GRUB and when my system restarted I got this kernel panic error. Kernel Panic: Attempted to kill init. <4>drives/usb/input/hid-core.c ctrl usb status -2 received drivers/usb/input/hid-core.c: timoeut initializing reports input: USB HID v1.00 Mouse [ARROW STRONG USB MOUSE] on usb-0000.00:1c.0-1 not sure what the error means. I'm trying to figure out what a kernel panic means and how to fix it. thanks. -Bryant