There are a lot of software to make windows genuine. But in real most of them are fake & don't works effectively. To make your XP Genuine don't need to download anything, just create it yourself. Its so simple, harmless.

Please read Steps attentively. Don't close this tab & just do so that described in the description step by step.
Step-1 Copy the following message:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion]
"CurrentBuild"="1.511.1 () (Obsolete data - do not use)"
"ProductId"="55274-640-7450093-23464"
"DigitalProductId"=hex:a4,00,00,00,03,00,00,00,35, 35,32,37,34,2d,36,34,30,2d,\
37,34,35,30,30,39,33,2d,32,33,34,36,34,00,2e,00,00 ,00,41,32,32,2d,30,30,30,\
30,31,00,00,00,00,00,00,00,62,fc,61,4c,e0,26,33,16 ,05,d3,54,e7,a0,de,00,00,\
00,00,00,00,49,36,c2,49,20,47,0c,00,00,00,00,00,00 ,00,00,00,00,00,00,00,00,\
00,00,00,00,00,00,00,00,00,00,00,33,33,35,30,30,00 ,00,00,00,00,00,00,65,10,\
00,00,74,99,dd,b0,f7,07,00,00,98,10,00,00,00,00,00 ,00,00,00,00,00,00,00,00,\
00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00 ,c4,ae,d6,1c
"LicenseInfo"=hex:e7,77,18,19,f8,08,fc,7d,e8,f0,df ,12,6e,46,cb,3f,ad,b2,dd,b9,\
15,18,16,c0,bc,c3,6a,7d,4a,80,8b,31,13,37,5a,78,a2 ,06,c8,6b,b9,d9,dd,cc,6a,\
9c,c5,9b,77,aa,07,8d,56,6a,7c,e4
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\WPAEvents]
"OOBETimer"=hex:ff,d5,71,d6,8b,6a,8d,6f,d5,33,93,fd
Step-2 Open and copy to Notepad.
Step-3 In notepad click "File" then click "Save As".
Step-4 For file type in the save dialog box select "All Files" and for the file name type in your name.reg or whatever you want. It doesn't matter as long as it has the .reg extension. (Just put your name in the place - "your name").
Step-5 Click "Save" to desktop.
Step-6 Double click the saved File thats now on your desktop.
Step-7 It will ask you "Are You Sure ?"
Step-8 Click on "Yes"
Step-9 Done.
Step-10
http://www.microsoft.com/genuine/downloads/FAQ.aspxStep11 Your windows is now validated.