I know I'm a bit late on this, but I'm seconding what rlkerJoe said about the 32-bit EFI. I believe if you have a Core Duo (not Core 2 Duo), then a 32-bit install should be perfect for that system. I can confirm that the 64-bit CPU and 32-bit EFI made everything a giant pain if you attempt to install almost any Linux distro without first being aware of that issue.
I did find a strange workaround for getting Linux on a mid-2000s MacBook with a 64-bit CPU and 32-bit EFI with minimal issues, although considering the whole 32-bit EFI thing, I'm still not sure why it works:
- Take a spare drive you have lying around
- Throw the drive into a 64-bit laptop or computer you have lying around (I used a ThinkPad my friend offloaded to me way back)
- Install Linux on the drive as normal
- Take out the drive with the Linux installation on it
- Put the drive into the MacBook and it should boot Linux with no problems
The only caveat is that I wiped the drive during the install process. If you're thinking of dual booting an older OS X, I don't know how that would work, although it should still be perfectly possible in theory. Again, I'm not sure why booting Linux this way ever worked for me, but I swear it did. I no longer own the ThinkPad in question to try it again, however.
For what it's worth, I tested this with a mid-2007 Core 2 Duo (Black MacBook).