German computer magazine C'T claims that by changing only 2 bytes from the file setupreg.hiv in Windows's XP Home kit, users can get access to certain functions only avalaible in Windows XP Professional, such as Remote Desktop, User management and enhanced security features.
C'T writes in its latest print issue (in German only) that you need to copy the root directory and the i386 directory of the WindowsXP CD to your harddisk, extract the Bootsector of your WindowsXP CD and change only 2 bytes in i386\Setupreg.hiv by using Regedit. In fact all you have to do is edit the binary key "default" and change "01" to "00" and "02" to "00" in HKEY_LOCAL_MACHINE\Homekey\ControlSet001\Services\setupdd, C'T claims.
There is one big drawback, though. Users won't be able to install Service Pack 2, unless they integrate SP2 in the installation CD. And that's probably too much trouble for most users, who of course are better off buying a legal version anyway. It is expected that Microsoft will change the setup files soon to prevent this hack. SOURCE