You can get a number of modding/extracting utilities here (my preferred one is DATBuilder):
http://www.terra-arcanum.com/downloads/

If you're referring to this guide, it suggests creating new files from scratch. If you do this, you won't need to unpack the original data. If you choose to extract and modify the original files, keep in mind that you'll have to use different line numbers from what's listed (just look through the file, note the pattern and extend it accordingly).