Well, if I look for GPT in the aid, what I get is:
"An unsupported partitioning scheme is in use on ..."
If you tell me where to look for it in the readmes, I thank you
In README.TXT (root of the DVD):
5.1.2 GPT disk partitioning schemes not supported
ArcaOS cannot access volumes created using a GPT partitioning scheme, and
requires a traditional MBR (Master Boot Record). Please ensure that your drives
are properly partitioned in this manner or that you are using a fresh drive for
installation, with no preexisting partitions.
This may not be quite as clear as it could be. It basically says "change the disk from GPT to MBR, then install ArcaOS". To do that, you need to back up whatever is on it, using a backup method that will allow you to restore to a MBR disk. Then boot to the ArcaOS installer, select System Management-> Disk-> Disk Utility. It will scan the disk, and tell you what it finds wrong. It should say something about GPT not being usable. One of the menu items in Disk Utility is to wipe a disk. use that (Disk-> Wipe disk information-> All disk information), and it will have you reboot. Now, run Disk Utility again, to add the basic LVM support, and then you follow the instructions for an empty (new) disk, to build appropriate volumes, using the Manage Volumes (Graphical) menu option (miniLVM). You also add Air Boot. Note, that if you do this while booted to anything other than OS/2, it will probably do it wrong. The other option, is to replace the disk with a new one (which may need the same treatment, but you will still have the original disk to fall back on).
GPT support is on the "todo" list, but it is not anywhere near the top of the list, so I wouldn't plan on waiting.
If it makes you feel better, Disk Utility is a custom version of DFSEE, designed to do exactly what needs to be done to install ArcaOS. Unfortunately, you are on your own if you wish to keep whatever might be on the disk before you start.