Somebody is just trying to make money on you.
There is no "secret code" to enable a USB keyboard.
All that is needed is for the USB ports to be recognized by your computer.
Now, if you are trying to get the keyboard recognized before the WinXP is loaded, then that means your BIOS must be able to read the USB ports. Not all BIOS' have the ability to read the USB ports during the POST (Power On Self Tests). Some BIOS' have a selection to turn that ability on. (I had one computer that required me to go into the BIOS and turn on "Legacy USB" so that a keyboard could be read during POST.)
Once the OS is loaded, the OS has to be capable to read the USB ports, and Windows XP is. Some people will tell you that SP1 is needed, that is not true. SP1 is only needed for the "Hi Speed" (480 Mbps speed) to function, otherwise it will only go at "Full Speed" (12 Mbps) which is just fine for a keyboard. (In fact, the USB Low Speed of 1.5 Mbps is more than sufficient for a keyboard, don't worry about the speed.))
For any USB keyboard to work, you of course, will need ports, plugs, and a keyboard to work. I have to assume you know how to troubleshoot them, like with item substitution. Good luck.