For wireless operations the Data Tank supports 802.11b and g clients and offers both WEP and WPA/WPA2 encryption. It also allows you to create ACLs (access control lists) where you can add MAC addresses of wireless clients and decide whether to block or allow access to them. Usefully, you can find the MAC addresses of logged in clients from the Information page and cut and paste them into your list.
The WAN port accepts an Ethernet connection or an ADSL or cable modem allowing the appliance to serve up Internet access to LAN systems. It protects them with a standard SPI firewall and supports four connection options with PPPoE and PPTP along with dynamic and fixed IP addresses. We had no problems using the latter mode with our direct Internet feed and had Internet access ready to go in a few minutes. You can select one system on the LAN and place it in a DMZ where it effectively sidesteps the firewall and port forwarding can be used to direct incoming users to particular services and systems.
We found shares easy enough to set up and for security you can create users and groups and determine whether each has read only or read/write access. Storage usage can also be controlled by assigning quotas in MB or GB to selected users. You'll find plenty of other features on tap as the appliance can act as a basic email server so you can set up your own internal mail addresses without the need for an ISP. The appliance uses FetchMail to retrieve mail from an external server and send it to selected accounts on the appliance but be aware that as it uses DDNS many ISPs may deem messages sent from these address types to be spam.
For media streaming the ever popular iTunes Server is not on the menu but the appliance runs TwonkyMedia for serving content up to UPnP devices but don't expect much help from the manual is configuring it. The appliance also runs MySQL so it can manage a database whilst the Apache web server can be used serve up your own web pages.
The Data Tank certainly delivers a pile of storage for the price and presents it in a well built desktop unit. Plenty of features are up for grabs as well, although backup facilities are limited and performance isn't one of its strong points.