PS3

Download cd image
http://gentoo.osuosl.org/experimental/ppc64/livecd/

Prepare your PS3 to boot another OS
Get the the otheros.bld file on http://www.kernel.org/pub/linux/kernel/people/geoff/cell/CELL-Linux-CL_20080201-ADDON/PS3/otheros/. Save it on on you memory stick at PS3/otheros directory:

(My memory stick is mounted at /media/usb) mkdir -p /media/usb/PS3/otheros cp otheros.bld /media/usb/PS3/otheros

Just install the otheros and boot, for more details on this see http://www.playstation.com/ps3-openplatform/manual.html.

Download the stage 4 and a portage snapshot
Choose a mirror at http://www.gentoo.org/main/en/mirrors.xml, and download this files: experimental/ppc64/stages/stage4-*-ps3_64ul.tar.bz2 snapshots/portage-latest.tar.bz2

And save then on the memory stick too.

Boot and Install
Insert the cd and start the otheros system. When the kboot prompt appears you can press 'tab' to choose the resolution that fit your needs.