Cool, the thing to keep in mind when using BootX is that the kernel it loads
does not exist on the linux partition, but rather in the Linux Kernels
folder in your System Folder. Make sure you have that copy stored there
(which sounds like you already do) and be sure to have the correct
System.map file (which you should have downloaded with the kernel) in your
/boot directory on the linux partition. Pointing vmlinux in the /boot dir
should not make any difference since the one that's loaded by BootX comes
from the Mac Partition. Also, make sure the system.map file name is correct
(screwed this up a few times myself)... System.map (case sensitive). Lastly,
did you also download the 2.2.15pre19 modules and copy them to the linux
partition?
Aside from verifying the correct kernel on the mac partition, System.map
file in the /boot dir, and the 2.2.15pre19 modules, you should be rockin.
Good Luck!