other options
Use the Add or Remove Programs tool in Control Panel
Click Start, click Run, type appwiz.cpl in the Open box, and then click OK.
Click to select the Show Updates check box.
Click Windows XP Service Pack 2, and then click Remove.
Follow the instructions on the screen to remove Windows XP SP2.
Use the hidden $NtServicePackUninstall$ folder
Click Start, click Run, type c:\windows\$NtServicePackUninstall$\spuninst\spuninst.exe in the Open box, and then click OK.
When the Windows XP Service Pack 2 Removal Wizard starts, click Next.
Follow the instructions on the screen to remove Windows XP SP2.
Use the System Restore process
Click Start, click Run, type %SystemRoot%\System32\restore\rstrui.exe in the Open box, and then click OK.
Click Restore my computer to an earlier time, and then click Next.
Click the date that you installed Windows XP SP2, and then click Installed Window XP Service Pack 2 in the Restore Point box.
Click Next, and then follow the instructions on the screen to remove Windows XP SP2.
Use Recovery Console
Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.
If you cannot successfully remove Windows XP SP2 by using one of the previous methods, follow these steps:
Insert the Windows XP startup disk in your floppy disk drive or insert the Windows XP CD in the CD drive or in the DVD drive, and then restart your computer.
Note When you receive the following message, press a key to start your computer from the Windows XP CD:
Press any key to boot from CD
Note Your computer must be configured to start from the CD drive or the DVD drive. For more information about how to configure your computer to start from the CD drive or the DVD drive, see the documentation that came with your computer or contact the computer manufacturer.
When you receive the Welcome to Setup message, press R to start the Recovery Console.
NoteMultiple options will appear on the screen.
Select the Windows XP installation in question.
Note You must select a number before you press ENTER, or the computer will restart. Typically, only the 1: C:\Windows selection is available.
If you are prompted to type an administrator password, do so. If you do not know the administrator password, press ENTER. (Typically, the password is blank.)
Note You will not be able to continue if you do not have the administrator password.
At the command prompt, type cd $ntservicepackuninstall$\spuninst, and then press ENTER.
Note After you complete this step, you cannot stop the removal process.
At the command prompt, type batch spuninst.txt, and then press ENTER.
Note The Spuninstal.txt file appears. As the file scrolls down, you will see errors and files being copied. This is normal behavior.
After Windows XP SP2 is removed, type exit, and then press ENTER.
Restart your computer in Safe Mode. To do this, press F8 as the computer restarts.
Note After you restart, the system may lock up with a black screen. (Your mouse will work.) In this case, restart again by turning the computer off and then back on. The second restart will let you to log on.
When your computer restarts, Windows Explorer (Explorer.exe) does not run, and the Windows icons and the Start button are unavailable. To resolve this problem, follow these steps:
Press CTRL+ALT+DEL to start Task Manager.
Click File, and then click New Task (Run...).
In the Open box, type regedit, and then click OK.
Locate and then click the following registry subkey:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\RpcSs
On the right side of the viewing pane, right-click ObjectName, click Modify, type LocalSystem in the Value data box, and then click OK.
Restart your computer
Use one of the previous methods to remove Windows XP SP2 from your computer.
and u cannot change the Boot Sequence from ur BIOS to boot from ur Original WINXP CD...(cuz u hav forgotten the password..lol 
