I remember having this same problem. What you want to do is in your admin area, click on 'Webmaster Mode', and then enable webmaster mode. Then, go to your catalog home, find somewhere where it says SKU, can click on it. A window will open that allows you to change the word SKU to Catalog #. Also, if you have any other text you wish to change, just navigate to the page it is on while in webmaster mode, click on the text if it is green, and edit it to your liking. Hope I was of help.
Jacques