Crashing Windows XP Manually

Method 1
You can crash windows xp system by simply holding the right CTRL key and pressing the "Scroll Lock" key twice." So you can have fun playing pranks on people by enabling this feature, I figure its for developers to test how things work when the system crashes, now you can crash it on the fly by enabling the feature described in the link.

1. Start regedit(to edit registry).
2. Navigate to:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\i8042prt\Parameters
3. Create a new DWORD value and name it CrashOnCtrlScroll
4. Right-click on this newly created value and click on Modify
5. Enter 1 in the Value data field and click on OK.
6. Close regedit and reboot your system.
7. Now you can blue screen (crash) your system by holding the right CTRL key and pressing "Scroll Lock" twice.

Note:

Your system may reboot or show a blue screen whenever this crash is initiated. If your system reboots after initiating the crash, and you want to see the blue screen, follow these steps:

1. Go to Control Panel > System
2. Click on the Advanced tab
3. Under Startup and Recovery, click the Settings button.
4. Under System failure, un check the option Automatically restart.

Method 2
http://everything2.com/index.pl?node_id=1257393