When using XP Computers that have Support Pack 3 on it, you may receive this error: "The remote computer requires Network Level Authentication, which your computer does not support. For assistance, contact system administrator or technical support.”
If you do, please click on the below link, run the Microsoft FixIT Package and reboot. Then the issue is resolved.
For more information on what this FixIT package is for: http://support.microsoft.com/kb/951608