A typical installation of 10.3 requires me to change discs during the middle of the install. One day while messing around with partitions, I noticed my Firewire DVD drive is visible in Disk Utility ... and during the install my external drive popped open when the second disc was needed.
So, in a nutshell ... I know if you have the LaCie Porsche designed external DVD-RW, you can put the second disc in it before you start, and then install OS X without interruption. This probably works with other external drives as well...
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040813031553831