I don't use Windows much so can't advise you there
But if I had a problem like this, the first thing I'd try to do is run a linux livecd and see if it would connect to the network. Knoppix, for example, will run in many circumstances: put it on a cd or usbstick (using LiLi, say), and boot from that
LinuxLive USB Creator
http://www.linuxliveusb.com/(1) If you can connect to your network when using a linux livecd or liveusb, the problem is probably something corrupted in windows -- maybe you need to remove and reinstall a driver? In that case, you might need to know what wireless hardware you have.
With a Knoppix or Ubuntu livecd or liveusb, you can open a terminal and type
sudo dmidecode | less which might give you the hardware info (you can navigate up and down through the long output with your PgUp and PgDn keys and you can exit dmidecode by typing
q). And if dmidecode doesn't actually give you the wireless info, it will probably at least get you the netbook model number and maybe some motherboard information that you can use when searching online for a driver. The manufacturer's website might be a good place to start. Ask the Windows users here for help with the driver issue
If dmidecode doesn't give enough info, you might try typing
sudo lshw | less in a terminal. This won't give you anything in Knoppix but with a different livecd or livecd you might get more hardware info (again, navigate with PgUp and PgDn and quit with
q): you're looking for something like "Wireless interface" (my acer netbook, for example, reports AR9285 Wireless Network Adaptor from Atheros Communications, when I do this off an Ubuntui liveusb)
Or maybe you have a corrupted configuration? Ask the Windows users here for help with re-configuring your network
(2) If you can't connect to your network this way, then you might have a hardware problem. I've bought two Trendnet wireless usb dongle @ $15 for adding wireless connectivity to some linux boxes, and I haven't had trouble with them, but newegg reviews suggest not everybody is happy with them. My linux boxes pick them up right away, but with Windows you might have to install drivers -- and perhaps reconfigure. Again, ask the Windows users here for help with that