I've now installed rEFIt on the Mac partition, and succeeded booting grub using the refit menu. The system starts to boot, and some kernel messages are briefly displayed.
Once the kernel re-initializes the display I get a black snowy screen. I haven't found a kernel parameter incantation that will prevent the graphics being re-initialised, so I can't get to a console to generate an 'lspci' listing, or other useful information.
Cheers,
Geoff Crompton