failing X after 8.04 upgrade

[skywise]

I'm running an ultra 10 with built-in video and X has stopped working after the box was upgraded to 8.04 from 7.10
What I'm getting when I startx is:
(II) Setting vga for screen 0.
(II) MACH64(0): Creating default Display subsection in Screen section
"Default Screen" for depth/fbbpp 24/32
(==) MACH64(0): Depth 24, (==) framebuffer bpp 32
(==) MACH64(0): Using XAA acceleration architecture

Fatal server error:
xf86MapDomainMem(): mmap() failure

Any idea what's up with this? Or how to get around it?

Sky