Well, I just crossed my own eyes because I let Gentoo upgrade GRUB, the bootloader, to the latest testing version, on Kristy’s computer. Booting to XP was fine, but the damn thing handed the Linux kernel a corrupted command line. So I started a download of the latest Gentoo Live DVD beta for x86 Linux, to use to re-install GRUB, but then I figured out a way in the broken GRUB to get the kernel a usable command line, and thus started up Gentoo with no problem. Then I re-installed the previous GRUB version, and I removed GRUB from the list of things for Gentoo to upgrade (which is how I kept things for a long time, until a few months ago).
Fortunately the last step eliminates Days Two, Three, and so on for at least a while. :)