Also download the Data ONTAP 7.3 documentation set from the NOW site. Many of the exam questions will come from information in those documents (you can also request hardcopy versions of the docs if you have a customer support contract or are a certified NetApp partner).
I also highly recommend the IBM Redbooks on Data ONTAP. The Redbooks are written less formally and contain a lot of diagrams, charts and screenshots so are easier to read.
http://www.redbooks.ibm.com/cgi-bin/searchsite.cgi?query=ontap