Here's the detailes.

1. Copy the root directory and the i386 directory of the WindowsXP CD
to your harddisk
2. Extract the Bootsector of your WindowsXP CD
a) *IMPORTANT* At this point, you MUST install any service packs
by slipstreaming them in as it will be in impossible to install
them later.

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.