Where does radius fit in?

I have been doing some reading re: radius.

When should one use radius?

I have read that radius is useful when one needs a centralized user/password
database.  I guess that would be good when one has lots of remote access
servers.

I have read that radius is good when one needs accounting.

We just need a dial in solution for 6 or so users.  No accounting is
necessary.  What are the disadvantages of using a simple ppp solution that
authenticates against the /etc/passwd file on a Linux box?

We were thinking of using a pci card with 8 modems.

Is radius overkill for us or is it a more secure solution?

Any advice/links to documentation would be useful.