I myself Have activated my Windows XP Today in this way.
Please Follow the steps properly to validate successfully.
I Have Tested it on XP SP1, XP SP2 and XP SP3 …

Follow the Following Simple Steps to Validate Ur Copy Of Windows XP:::—
STEP 1:
Download Windows Key Changer Here.
Download:
http://rapidshare.com/files/281122691/KeyChanger_Windows.rar
Mirror:
http://www.megaupload.com/?d=F0AVSDE0
(Only One Of the Keys Provided For Above App Works, So Try Both)
STEP 2:
The File U Downloaded Above(KeyChanger_Windows.rar) also contains The Genuine Windows Key.Change Ur Windows Key Using This Software to This Key.
(RECOMMENDED–Plz Don’t Change Any other Fields Other Than The Key)
STEP 3:
To Check For Validation, download WMP 11 setup. It Requires validation in the beginning.
Let it Validate, if the validation is successful here(in WMP 11 Setup)then move to the next step otherwise not.. IF it is not Successful then , Repeat the above two steps again & Carefully.
Download:(WMP 11 Setup)
http://www.filehippo.com/download_windows_media_player/
STEP 4:
Now, that u’ve successfully validated in the WMP 11 Setup.Go to the following Page to formally validate ur XP.(for English Users only). It takes a few minutes and u r done.
Link:
http://www.microsoft.com/genuine/validate/ValidateNow.aspx?displaylang=en
NOW ENJOY UR VALIDATED XP…
If the procedure won’t work then, Comment here. The possible reason may be that the Key may Expire.Plz carry out each step carefully.I’ve myself Done it so i’am 100% sure it’ll work.
IF U DON’T HAVE WINRAR TO EXTRACT FILES–DOWNLOAD IT HERE
http://rapidshare.com/files/282646068/WinRAR_3.90_Pro.-vipul0092.zip
