Hi there.

I'm not sure it's gonna help U, but for what I remember, I never managed to boot from a gentoo ia64 CD, but it was long ago now... (about 2 years !)

When I made my install, I had to download and install a Debian (the only one CD I managed to boot with !), and after that, install gentoo in a chrooted env...

Maybe you could try having a similar approach if you got time to spend and enough disk space :)

However, good luck with your install :)