Disable Error Checking at Startup

Start/Run/Regedit. In the right pane, delete this entry: BootExecute autocheck autochk*

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager

Disable/Remove Serious Error Message Upon Boot

Start/Control Panel/System/Advanced/Performance/Settings/Advanced/Virtual Memory/Change/Set to 0. Reboot/Reset Pagefile to System Managed Size.

Disable Windows XP's Windows Tour Prompt for all Users

Start/Run/Regedit. Navigate to...
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Applets

In the right pane, locate Tour (if it doesn't exist, add it. Edit/New/Key. Then select New Value and set it to 0).

To set the same option for users, navigate to...and repeat the above steps.
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Applets

Disable Unnecessary Programs at Startup

Start/Run/Regedit. Right Click/Delete unnecessary programs listed here:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Runonce HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

Disable or Enable Boot Defrag

Start/Run/Regedit. Navigate to...
Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Dfrg\BootOptimizeFunction

Select Enable in the right pane/Right Click/Modify/Change Value to Y to enable, N to disable. Exit/Reboot.