Hosts.all/Hosts.deny vs. a firewall?

[William Jensen <jensenb@charter.net>]

So far I have the following setup:

hosts.deny:

ALL:ALL

hosts.allow:

ALL: my_work.domain

My intention is to prevent everyone from the 'outside' from reaching my box.  I do realize that anyone in my_work.domain would also be able to get at it.

It is my understanding that this will prevent anyone not in my_work.domain from getting to my box with telnet, ftp, etc.  Is this correct?  Is this secure?  If this is indeed correct could someone tell me why I would need/want a firewall and/or what benefit it would provide me over what I already have setup?  More specifically how does a firewall differ from using the hosts.allow/hosts.deny files as I described above.

Appreciate any advice on this...

Bill