I have been looking in to nast because I require it for auditing my home network

I am looking to use nast to capture strictly usernames and passwords
I was wonder if anyone can direct me to a link that would have this information and I also wanted to know if anyone had an pcap filters that they can email me at napisani@yahoo.com

im not sure that I really under stand how to use nast is this the command:

nast -ipdxf something.pcap