This should be fun. I was thinking about setting up centralized authentication, authorization and accounting on my home network, but I keep worrying about what would happen if my account gets compromised (password guessed).
If I had time, I'd evaluate LDAP, Samba and Radius. Let us know how yours goes. Take notes! ;-) I have worked a bit with Radius. From what I have seen it is pretty bullet-proof. Someone would have be doing a lot to sniff those packets. I know the accounting and everything on their is pretty sweet. Most Radius products will o a simple easy import into something like a spreadsheet (*.cvs files are most common I think) to assist with your accounting, but I imagine any database will do. Haven't worked with LDAP (but would like to play) really so can't add any insight there.
