I am new to Ubuntu, i installed it in an old PC and now it works GREAT!!! My Macbook pro has a glitch and refuses to run Mac OS X, so i installed Windows, and i really want Ubuntu since Windows is not for me. Here's the problem(s) my drive only READS DVDs, if i put a blank in it, it will ignore it and my mac has the updated EFI, so no booting from a USB connected device! I also tried Wubi, but then i cant make it a FULL partition and get rid of windows!!! Thank you!
If I understand, you want to download a new version of Ubuntu and put it on some media and boot from that media to install it to the whole disk on your Mac OS system. You are constrained in that the media you can write to you can't boot from and you can boot from the CD/DVD drive but have no means of writing one. Further, I assume you can't write a CD from that old PC running Ubuntu.
If all of that is correct, I can see three choices. (If it's not correct, please correct me by editing your question).