On the right side of the taskbar, you will see a wireless network icon like the one below. Click on it.
A window with available network connections will open. As you can see from the screenshot below, the list is split by the type of available network connections. At the top you have dial-up and virtual private network (VPN) connections, while at the bottom you have a list with all the wireless networks which Windows 7 has detected. To refresh the list of available networks, click on the button highlighted in the screenshot below.
You can scroll down through the list of available networks. If you leave your mouse cursor over a network for a second, you will see more details about it. Windows 7 will show the following: network name, signal strength, the type of wireless security used (if any) and its Service Set identifier (SSID).
Once you decided on which network to connect to, click on it. If you plan to use that network in the future, make sure you check the box that says 'Connect automatically'. This way, when you start your laptop next time, in the same area, it will automatically connect to this wireless network without requesting any manual intervention. Next, click on the Connect button.
NOTE: be cautious with wireless networks which have no security enabled. They can be used to steal personal data. If you connect to such networks make sure your security solutions are turned on.
After a few seconds, you will be asked to enter the security key. Ask the administrator of the network for the wireless security key or, if you are in your own home network, take it from the control panel of your router. If you are in a public place, it is best to check the 'Hide characters' box so that other people don't see what you are typing. Then type the security key and click on OK.
If you typed an incorrect password, Windows 7 will request you to type it again and again until it matches the password of the network you are connecting to. If everything is OK, Windows 7 will connect to the network you selected using the given security key. When the connection is successful, the wireless icon from your taskbar changes as shown below.
NOTE: this procedure works only if your wireless adapter is enabled. If it is not enabled, you won't see any wireless networks being available. The procedure of enabling the wireless adapter is different for each model of laptop.
If you are connecting to a wireless network which you do not own, make sure you know the password for it from its administrator. If you do not know the password of the network, your connection will never work.
You installed the boot camp drivers right? On the Windows side? They are on any Mac OS X disk, 10.5 and later. I know you are running 10.7.2 but if you have a 10.6 disk you can pop it in while booted to Windows 7 and it will start up with a autorun.ini and has an executable file that will install all of the mac drivers for Windows 7 (bootcamp). It sounds like your airport card is not being recognized by Windows. If you did install the bootcamp drivers, then I would power cycle the router. Unplug the power cable from the back of the router leave it unplugged for 15 seconds. Plug it back in and see if your network shows up.
What kind of router do you have? What encryption are you using? WPA, WEP, WPA 2 PSK?
What happens when you plug directly into the router via and ethernet cable? Does it register an IP address? Do you at least get a self signed IP if not receiving one from the DHCP server? Self signed subnets are 169.x.x.x.
Let me know.
If it cannot connect, then did ANY Windows updates get installed?
Did you follow the how to guide and manual?
If you go to Device Manager for Network, can you:
Sometimes a driver gets installed that breaks support.
Q: did you have network access and lose it at some point?
Some people have trouble after installing Apple drivers; more common to have wifi issues and need to find a new driver.
My "Vista Inside Out" book recommended to setup a WIRED connection first, get that working and configured and only then setup wifi with the setup assistant in Windows.
Connect directly to the modem via wired connection and bypass the router even.
Some network devices may not work with Windows 7 if they are 3-4 yrs old.