Lenny will rock you!
It took two months, but finally the hard disk replacement for the MacBook has come. Of course I'll think twice before ordering anything else from Alternate (ES), not to mention the fact they served the SD cards without micro adapter (which means they're useless to me)...
Anyway that was not the point. The point was, as you may have guessed, I tried the latest Debian installer for Lenny, which is beta 2 at this moment:
First, the niceness of jigdo downloading the first amd64 DVD image flawlessly and without a single retry.
Second, wodim burning it without error in a disc I had forgotten for two weeks inside the drive.
Third, being able to swap broken disk and the new one despite Apple's instructions to change it forgot to mention you need a very small torx screwdriver to detach the drive from the pulling tab it has (it's located deeply inside and the tab is necessary for removing it).
Fourth, partitioning and installing MacOS X... well, last time I tried dual-boot it didn't work at all, so I had to try again, and with a 320 GB disk using less than 10% for a proprietary OS doesn't look like a great loss ;-). Partitioning is a bit tricky, as detailed in the wiki, but the Disk Utility method worked fine for me. Scheme was 30-2-288 (more or less), you'll discover later why. Worth to mention that the MacOS X showed a lot of upgrades after setting up the wireless, including an EFI firmware upgrade (new boot ROM version is MB21.00A5.B07). I installed all of these before continuing.
Fifth, installing rEFIt, though this one has no trick...
Sixth, rebooting and installing Lenny beta 2 from the DVD. To run an encrypted system two partitions are required, one for /boot (unencrypted, bootable) and other for the encrypted filesystem, hence the two partitions defined. I forgot to add a swap partition, but a swap file can be added later. The uswsusp package will warn about lacking swap, but seems it does complain even if you have a swap partition. You have to avoid installing bootloader at this point, because MBR layout is not the same that GPT (which Disk Utility wrote), hence bootloader installer would be misled.
Seventh, rebooting and entering rEFIt's disk utility, which immediately offers to resync MBR to match GPT layout. Wonderful.
Eighth, restarting Debian installation again, having to reinstall, because the filesystem inside the big encrypted partition is not recognized and had to be reformatted. Not a great problem though. Finally installing grub in the /boot partition, and finish installation.
Upon restart, rEFIt menu shows both MacStuff and the penguin, and both work fine... in fact I'm writing this from the new Safari in MacOS X, because the wireless card in Debian is still to be configured, but that's another story...
Note: if you're going to try this, first of all read the wiki like I did, it has been improved a lot.