you will need two pieces of hardware to get you going wirelessly:
1- Wireless Router
2- Wireless Ethernet card
Your DSL modem has three connector at the back..Power, Telephone cable (or RJ11 connector), and Ethernet connector (RJ45 Connector).
You need to buy a wireless router, it come with a Ethernet cable, one end of the cable goes to the back of the DSL modem and the other end goes to the back of the Router (there any usu all 5 ports at the back and one of them will say "WAN" that's where you want to plug incoming cable from the DSL modem).
follow the link to home Wireless networking product on Dlink site:
http://www.dlink.com/products/category.asp?cid=1&sec=1
Look at the product, and make sure your Wireless Router speed matches the Wireless card you buy.
Wireless routers have easy installation guide and so does wireless cards, after purchasing the hardware, try to do if yourself, if you run into any problem then drop us a line and we will follow up with you.
Cheers