Did you follow the next steps?
Try to change the channel on the Airport base station from Automatic to a channel between 1 and 11.
To configure the PC for the network:
- Boot up the PC and then right-click the wireless (adapter in my case) software on the menu bar.
- Select Refresh or Find Available Networks then select the SSID you want to join.
- Once the "Current Network Info" appears, click "More Settings."
- Under "More Settings" in the wireless LAN configuration window:
- for TX Rate choose "Auto"
- for SSID choose "(your preferred network)"
- for Network Type choose "Infrastructure"
- for Encryption choose "WEP"
- for Authentication Mode choose "Shared Key"
- Then click the "Apply" button
- Click "WEP encryption key setting"
- Enter "WEP" password, which is a 128 Hex Key in the WEP Encryption key setting on just one line. There may be half a dozen lines, but only one has to have the passkey, which is described in the section below.
- After you get the Password/Hexkey from the Mac (see below) and have it entered on the PC, then UNCHECK the box "The key is provided via 802.1x authentication".
- Then click Apply.
If you have the new 802.11n Airport Extreme it is possible to be in the
wrong mode, in other words running in 802.11n or 802.11a and your Windows laptop can only access 802.11b or 802.11g networks. Check the wireless radio mode of the Airport base station.
Though Windows XP SP2 supports WPA and WPA2 encryption not all wireless hardware does, especially if it is older hardware. Check that your hardware actually supports the use of WPA or WPA2.
Also check:
Ensure that the Enable IEEE 802.1x authentication for this network check box is
not checked.
If you are using AEBS firmware 5.1.1, 5.2 or 5.3. All other versions of the firmware allow
Open authentication, firmware 5.4 allows both Open and Shared.
Ensure Network Authentication (Shared Mode) box is ticked or the drop down box is set to
Shared if you have installed various XP updates.