Due to the size of the Xubuntu ISOs, they no longer fit on a standard CD, this guide will help you if your BIOS doesn't support booting off of USB drives by showing you how to use Plop bootmanager.

The Plop bootmanager homepage is at http://plop.at and you can download the most recent version at http://www.plop.at/en/bootmanager/download.html and you shouldn't need a special edition. (plpbt-5.0.14.zip 2012-02-11 Plop Boot Manager 5.0.14 at the time of this writing.)

It's generally the same process as documented at https://help.ubuntu.com/community/BurningIsoHowto Main contents of the downloaded archive should be:

1README.TXT  Instructional Readme.
plpbt.bin    Boot manager binary
plpbt.img    Boot manager floppy disk image
plpbt.iso    Boot manager cd iso
plpbtrom.bin Boot manager rom file for the bios

doc/          Documentation
experimental/ Experimental versions
pcmcia/       PCMCIA version of the boot manager
Linux/        Linux related programs
Windows/      Windows related programs