SpAceTraNce

For Pro: Go to Start/Administrative Tools/’Local Security Policy/Security Settings\Local Policies\Security Options
Accounts: Limit local account use of blank passwords to console logon only. This is enabled by default, disable it.

For Home: (Keith Miller) Go to Start/Run/Regedit and navigate to this key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa

Value name: limitblankpassworduse, Type: REG_DWORD, Data: 0 (disabled) 1 (enabled)

For Home: Run Scheduled Task without a Password (Line 67)
http://www.kellys-korner-xp.com/xp_tweaks.htm

How to Enable Automatic Logon in Windows
HOW TO: Modify Scheduled Tasks in Windows XP
Task Scheduler Does Not Run Tasks When “Run As” User Account Has No Password