For what it's worth: from the Gentoo Linux installation instructions (http://www.gentoo.org/doc/en/gentoo-x86-install.xml):
"Important: If your boot partition (the one holding the kernel) is ReiserFS, be sure to mount it with the -o notail option so GRUB gets properly installed. Make sure that notail ends up in your new /etc/fstab boot partition entry, too."
I haven't tried this myself though (I took the easy route and used ext3 like rock).
Hope it helps,

Neje