For Debian on PC I used this guide: http://www.debian.org/releases/stable/i386/ and used this iso: http://cdimage.debian.org/debian-cd/current/i386/iso-cd/debian-6.0.1a-i386-netinst.iso
For Ubuntu I used 10.04LTS 32 bit desktop edition but others have reported success with others 10.04 variantssuch as the server edition (32 bit). 11.04 seems to have some issues. For now development focus is on 10.04 as it is an LTS.
For SheevaPlug I used this guide: http://www.cyrius.com/debian/kirkwood/sheevaplug/install.html