I can't believe I'm seeing this when there is a thread permanently stickied to the top of this forum literally called "The PowerPC Linux Wiki". It exists to detail information, walthroughs, guides, and links in order to make life easier for those running Linux on a PowerPC Mac so that they would not experience the frustrations and fruitless, unanswered questions I had when first learning and easing into Linux.
An insane amount of knowledge, effort, care, and trial-and-error were put into it over the course of almost a year now, and it amazes me every time somebody waltzes in asking questions about Linux that they could have had answered had they instead bothered to refer to it.
@Frank Ciampa Champ,
@wicknix has similarly put quite a lot into Lubuntu 16.04 Remix to ensure it operates as smoothly and as trouble-free as possible on these very machines. I suggest using that in conjunction with what's available on The PowerPC Linux Wiki for troubleshooting and proper setup. It has sections dedicated to USB booting and manual partitioning.
My advice is to wipe the disk clean (Yellow Dog is old and useless), try booting from USB again with the Wiki's instructions, and manually partition Lubuntu by selecting the "Something else..." option in the installer. The manual partitioning guide meant for the CLI installer should translate over fine to the graphical Ubiquity installer, as not a great amount is different between the two. Should any questions or inquiries remain that are not helped by The PowerPC Linux Wiki, any one of us would be perfectly happy to offer assistance to the best of our abilities.