Is the bios set to be able to boot from USB?
Re-read the original post.
on boot-up it still goes direct to XP, with no option to choose which OS.
Sounds like the last step of the installation didn't quite go to plan...(do you remember seeing screens referring to MBR, boot records, boot loaders or some such ? If so, do you recall what you selected ? ).
Other than that, unfortunately I'm in the same camp as MG23, all my Linux installs are either bare-metal or virtual machines....so I don't know much about parallel installs.