use registry hack to enable or disable Windows XP task manager

As part of the enhanced management available in Windows 2000 and Windows XP, rather than risking a registry change, as an administrator you can enable or disable Windows 2000 Pro or Windows XP Pro's TaskManager using Group Policy Editor. This can be applied to the local policy. Note: if you are trying to override your organizations group policy, you can't. As soon as you re-authenticate to the domain, the domain or OU Group Policy will rewrite the registry setting. But if the TaskManager was accidently disabled or you need to control this item for a set of standalone boxes this is for you:

Click Start
Click Run
Enter gpedit.msc in the Open box and click OK
In the Group Policy settings window
Select User Configuration
Select Administrative Templates
Select System
Select Ctrl+Alt+Delete options
Select Remove Task Manager
Double-click the Remove Task Manager option
And as I mentioned above, since the policy is Remove Task Manager, by disabling the policy, you are enabling the Task Manager.

The source:
http://www.windowsnetworking.com/kbase/windowstips/windowsxp/usertips/customization/enabledisabletaskmanagerinwindowsxphomepro.html Answered Jul, 03 2011

press ctrl+alt+delete at the same time. Answered Jul, 11 2011

1. Click Start -> Run, and then type regedit, then press Enter. In Windows Vista, just type regedit in Start Search, and press Enter.
2. Navigate to the following registry key: Answered Apr, 10 2011

Well, I hope this way will help you.
1Start Windows in your normal manner.

2 Click "Start." Then highlight and click "Run."

3 Type "REGEDIT" into the text bar and press "Enter."

4 Navigate through the registry, looking for the following directory: "HKEY_CURRENT_USER \ Software \ Microsoft \ Windows \ CurrentVersion \ Policies\ System."

5 Right-click on the "HKEY_CURRENT_USER" and click "New" from the context menu to include a new string. This is only necessary when the necessary directory is not currently present in the registry. By default, Windows XP Home Edition does not include the necessary directory string.

6 Click on the "DisableTaskMgr" phrase and delete it. This is the simplest way to do it, but it makes it more of a challenge to repair in the future. You will need to manually reenter the string if you didn't back up first.

7 Change the numbers in the boolean section of the entry from one to zero. This will enable the Task Manager in Windows XP. Note that the zero is essentially equivalent to a positive entry in this regard, as the initial string is a negative.

8 Change the string manually from the "Run" window of the Start Menu, without having to access the Registry Editor. Simply type "REG add HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\System /v DisableTaskMgr /t REG_DWORD /d 0 /f" into the text field and press "Enter."
The reference web site:http://www.ehow.com/how_2052294_enable-task-manager-windows-xp.html
. Answered Mar, 23 2011