How would I be able to perform a minimal install of xubuntu for a PowerPC?
My computer cannot read DVD's, and the xubuntu iso file is 744MB (I can't burn it to a CD).
Is it possible to burn it to a CD?
Try the minimal CD from here (choose the powerpc options) - when booting from the CD, use the option "install" and follow and accept the text prompts. Eventually you will be offered a selection of stuff to install - one of which is xubuntu.
Remember to be connected to the internet via a wired connection - the minimal CD downloads all its stuff from the internet.
I'm not sure where you got your .iso from. Mine is 687.8MB from the Xubuntu home-page and fits on a CD.
Try downloading the file from the main Xubuntu page here and burning that .iso to CD instead. All of the official Ubuntu derivatives work to keep the disk size small enough for CD's, so unless something is very wrong, you should be fine to burn that to a CD.