Change Windows XP Home to Windows XP Pro

Needless to say that the legitamacy of this hack is dubious and you won’t get any support from MS for doing it.

You can’t change an installed Windows but only your Installation CD (or even a recovery CD in case the manufacturer had not left out important parts). So here’s how it gets done.

1. Copy the root directory and the i386 directory of the WindowsXP CD
to your harddisk
2. Extract the Bootsector of your WindowsXP CD
3. Change 2 Bytes in i386\Setupreg.hiv :
a) Open Regedit
b) Highlight HKEY_LOCAL_MACHINE
c) Menu: File -> Load Structure -> i386\Setupreg.hiv
d) Assign an arbitrary name to the imported structure e.g. “Homekey”
e) Goto HKEY_LOCAL_MACHINE\Homekey\ControlSet001\Services\setupdd
f) edit the binary key “default” and change “01″ to “00″ and “02″ to
“00″
g) Highlight “Homekey” and select menu: File -> unload structure
4. Burn your new XP Pro CD
5. Install WindowsXP as usual. Your XP Home Key will work.

source: Gizmodo