here's a list of the things I did to successfully install Windows Vista and Linux Slackware 14 on a MBP 5 (after a lot of tries).
1) booted up using Slack CD ROM, deleted the GPT using the zap command
2) then booted up using the Win CD and installed using some space of the hard disk. And then I made sure the computer would boot it.
3) then booted up under Linux, repartitioned using fdisk, created swap and root filesystem, but I left marked as bootable only the Linux partition
4) setup as normal
5) when asked by lilo, I choose Automatic setup and install into MBR
Apparently Mac doesn't need the GPT or it's rebuild automatically on reboots. But MBR needs only one partition active.
