I built xorg from latest CVS to try this out on an altix-based Prism deskside
machine.  When I started the X server, I got the error message
"Kernel 2.6.11 or better needed for Altix support"

I was running a version of 2.6.12.  

It appears there is just a small problem with this file:
programs/Xserver/hw/xfree86/os-support/linux/lnx_ia64.c

On line 54, various checks are done to see if the system is really an Altix.
Those are fine.  But we seem to check if the kernel verson is equal to
2.6.11 rather than >= :

         if (!strstr(utsName.release, "2.6.11")) {
            ErrorF("Kernel 2.6.11 or better needed for Altix support\n");
            return NONE_CHIPSET;