Xorg not working on new install

[Harmon Seaver <hseaver@gmail.com>]

    I just installed debian 4.0 on my Umax Supermac S900. It has a
NewerTech G3 upgrast installed debian 4.0 on my Umax Supermac S900. It
has a NewerTech G3 upde card (333mhz), and 528mb of ram and a ATI Rage
128 video card with 16megs of video ram.
    GDM starts up X and it seems to work, gives me the login screen,
mouse works, and lets me log in or try different sessions, etc. But very
quickly after logging in, it gives an error message about my "session"
quitting. Trying the other session choices fails also. Checking the Xorg
logs shows an error "INVALID IO ALLOCATION". Same thing happens with
killing off gdm and trying startx.
    The problem has progressed to causing a system crash now when trying
to start X. One thing I notice when booting is that an agpgart
interface, although obviously this old supermac doesn't have an agp slot.

-- 
Harmon Seaver