help!

I realy need to install Red Hat 9 and I've already installed Windows XP(I need it for school).

Would it be a good idea to get an external hdd and install Linux on it (I don't want to make a new partition on my hdd with XP) and how I should set boot order (I have only CD drive) in Setup I can set boot from CD or boot from hdd.

I'm quite new in this, so any advice would help!!!