Your computer connects to an access point that broadcasts its SSID instead of an access point that does not broadcast its SSID

When your Microsoft Windows XP Service Pack 1 or Service Pack 2 (SP1 or SP2)-based Wireless Zero Configuration (WZC) client computer is in the proximity of two wireless access points, and one of the access points is broadcasting its Service Set Identifier (SSID) but the other is not, your computer always connects to the access point that is broadcasting its SSID. This occurs regardless of the preference order of the networks that are configured on the Preferred Networks list.

Additionally, when your computer is connected to an access point that is not broadcasting its SSID, and another access point that is broadcasting its SSID is enabled nearby, your computer automatically connects to the access point that is broadcasting its SSID.

Wireless Zero Config Service (WZC) always tries to connect to a broadcasting Access Point that is listed in the Preferred Networks list first.

This behavior is by design.

The Windows XP WZC service dynamically selects the wireless network to which your computer connects based either on your preferences or on your default settings. This includes automatically selecting and connecting to a more preferred wireless network when it becomes available. If no preferred wireless network is found nearby, the WZC service configures the wireless adapter so that there is no accidental connection until the wireless client is in range of a preferred network. For more information about the WZC service, visit the following Microsoft Web site:Disabling SSID broadcasts is not a sufficiently strong method for securing a wireless network.