Connect to a domain with a wireless router

Hi my friend has a small business with 6 computers all connected to a domain on a server. The six computers and the server are connected to a switch. He bought a laptop sometime ago and connected it to the domain and has access to the server and internet through an Ethernet cable plugged into the switch. He wanted to be able to carry the laptop around the store so he bought a TP-Link TL-WR841HP wireless router. He thought it would be simple to hitch up but he has run into problems.
Can you please give me the steps he needs to get it to work. He's running Windows 7 Pro 64 bit O.S.
Thank You

If you have an existing DHCP server (or router), then you need to convert the TP-Link router into a WAP (wireless access point). Basically, that means disabling DHCP on the router and changing the router's static IP.
http://www.ezlan.net/router_AP.html

Or he could could swap out the router that is connected to his ISP already.

You'll need to provide more details about the setup, or else we are just guessing.