Bootloader woes

[Grant]

Hi all,

Somewhere along the line, my PRAM configuration has changed and I am no 
longer presented with a list of OSes to boot from - it jumps directly 
to OSX.

This would be OK, if imperfect, except that when I boot using "option" 
- and am presented with a list of alternatives (including YDL) - it 
begins to boot but immediately the screen goes grey and the following 
text appears:

...OK
copying OF device tree .......done
initializing fake screen:  NVid, NVmac
calling quiese ..........

==> freeze <====

Any advice on what's going on and how to fix?

Grant