This is very odd.
I've installed the version 1.40 drivers for my DWA-552 on Windows XP SP3. The drivers and configuration utility both work fine, but as a result of installing the upgrade, XP's fast user switching feature has been disabled. Windows expressly identifies wlangina.dll as the cause, and 1.40 notes a fix involving that very file.
So, what gives? How can I fix this? Going into User Accounts in the Control Panel is fruitless, as Windows will not allow me to re-enable fast user switching.