creating an external hard drive

If its not gonna be a boot drive, it'll need no operating system. In fact, unless you're thrilled by twiddlin' and tweakin', you'll be better off without an OS on the external drive. I employ several external hard drives, FireWire/USB2.0, and none of 'em have an operating systems. I use 'em primarilly as repositories for the output of applications ... a place for finished work, more or less. They even get moved around from 'puter to 'puter to facillitate transfer of really large files; its much quicker to physically connect the drive hosting the file to be transfered to the destination machine than to transfer the file from machine to machine over my network.