If I join local NSSLHA, am I automatically enrolled in national NSSLHA?

No. National NSSLHA requires separate registration as well as separate payment of dues. 2011 dues are $60 for one year. Please see this site to join national NSSLHA.

Do I have to join national NSSLHA or can I just be a member of local NSSLHA?

No, but we strongly recommend you join national NSSLHA if you plan on going to graduate school, especially if you are planning to attend graduate school here at Ole Miss. National NSSLHA has many benefits to joining--access to ASHA journals (useful for class projects and research), reduced rate on attending the ASHA convention (second year graduate students at Ole Miss typically attend as a group), and a discount when applying for your CCC. Please see this site for more benefits to national membership.