Well, as Dev has said it u need a router.
A "router" can be a specialised device or as well a computer which runs routing software. If u have a not used low end machine, that will do it, and u dont have to spend a cent on a router. Of course if u chose to buy a Router then u dont have to install/configure its os/software (well, not as much as for example a linux).
There is two tipe of Routers to share your adsl/cable connection, one which require an additional adsl modem, and one which doesnt. But booth of them is same in that way, u can attach them to your Ethernet network (some versions even come with a built in switch). These routers runs NAT so, any computer connecting to them can acces the internet.
But be warned, the ones without the need of additional dsl modem costs much-much more... If you are given a modem by your isp, then i suggest u to use the cheaper option, provided u dont have a serious reason not to do so.
Well, as for connecting the devices, if u have a switch already, u can simply connect the router to your switch, and woila, evrithing works. And if u want to connect your ADSL Modem to the switch, that will work also, but then u have 2 option to chose if u want to connect to the net:
1: u run your own router (a pc in this case), which will connect only to the modem, and the pc will give NAT service to the other computers on the network (of course the router pc must be powered on all the time)
2: u can connect with PPPoE driver (in most cases) directly to the dsl modem from any computer. But be warned, usualy the EULA wont allow multiple connections (this kind of connections!) in the same time, for the home users. So this means if your ISP allows it, you can connect with multiple computers to the dsl modem (i can connect to MY modem with 3 computers in the same time, in your case its can be different) without another device. Of course the summarised speed will be the what you paid for.
And finaly about that D-link. Well each router offers different kind and variaty of service (firewall, DMs, port forwardings, etc), its up to u to decide waht you NEED, and what u can AFFORD to buy. Check a lot of device, maybe there is one which cheap and meets your requirements. Usualy the cheapest solutions will do it.
Well, have fun with your dsl