I put in an invisible zipper (in a Barcelona skirt) using this tutorial:
http://www.simplicitynewlook.com/index.php?main_page=page&id=92 The instructions are for using a regular zipper foot (rather than the special one called for on the package).
Because I was on crummy dial-up at the time, I couldn't get the pictures, but I was still able to get the zipper in without swearing a blue streak (pictures in the Barcelona pattern were helpful). And it is (mostly) invisible.
Good luck!