I do not think you need to upgrade either,
For 15 workstations no database server and no networked business application, W2K Server running microsoft exchange server for your email. Does your DSL provider allow you to connect an exchange server to your line? Most do not like it for the potential of banwidth usage. They will probably tell you that you need a T1 line. So your best bet to outsource mail server.
The most secure way to connect your network to the internet is to rout your gateway. In other words configure a router with your gateway's IP address than directly connecting your file server. You have another level of security with a router.
It's cheaper to outsource a mail client than it is to manage your own for a one-server/15 workstation network. I am assuming you are running a workgroup not a domain.
Good Luck,
Russell Smith
http://www.mawebcenters.com/kate123w...net/index.html