You should be able to. Ubuntu (In fact, almost all Linux distributions) comes with it's own bootloader (Usually GRUB).
i was just wondering is it possible to create a second partition to install ubuntu on a computer with windows on it? i would like to try it as a system instead of using it with a VM..
Even if you don't have free space on your HDD, I think that Ubuntu's installer should have an option in the disk partitioner to resize existing partitions.
Unmodified SCPH-77006 with SM 3.6
SCPH-39006 with M-chip modchip, SCPH-10281 NA and refurb Seagate 80GB HDD
SCPH-10000 v1.00 with SCPH-10190 PCMCIA NA and SCPH-20400 HDD unit