Hmm. Alright. I'll ask the list.
In the meanwhile, I now have a hd that looks thus: half is ext3, the other half ext2. Both use Debian. Can I turn the other half in to XFS,
take a little bit of that partition and turn it in to an ext2 /boot and still have GRUB work? 
If that is not clear, I mean this:
|-----------------------------------------|---------------------------|-----|
|     ext2, / and boot           |   XFS, /               |/bo|  <--ext2
|                                         |                           |  ot| 
|-----------------------------------------|---------------------------|-----|
I would install GRUB to the MBR, as usual. When booting in to ext2, I would use that. When booting in to XFS, I would boot in to /boot? 
Or, should I just try it and see what happens? I'll still be able to boot in to ext2 no matter what, right?
Thanks much.