Note that the original post was for the physical lock the HP workstations have on the side panel to prevent access to the inside of the workstation. the post below refers to the microsoft Windows Key used for OS activation and while not directly related to the original poster's question might be usefull nonetheless
note that the xw6200/8600 systems were EOL before windows 7 was released, so offically the win 7 activation changes do not apply when talking about XP or previous OS's
the xw6200/8600 systems were made when the MS serial label on the side was a actual valid key and each one was a unique Retail key, and would activate windows on any hardware configuration
later on MS stopped allowing windows activation via this method
there were many cases where a buyer of a floor model would at some point try to reformat the system and use the key from the label and be told by the Ms activation servers that the key was allready in use because someone had copied the key and used it previously.
the later ms key labels have a number on them (prooving ms got it's cut from the windows OS) buy it's no longer a valid retail key, with the newer serial labels you have to call ms and either speak to a person, or use a automated phone service which takes that key from the side notes the hardware it was orignally attached to HP/Dell/Lenovo and so on and confirms the new hardware closely matches the original. IE-Dell to Dell, HP- to HP.
if you had or have a tier one system that performed auto activation of the OS using the MS vender assigned windows key that used the bios string, plus a vender certificate then you usually did not even need to worry about Ms activation keys. the venders OEM OS disk was all that was required to install/activate windows
http://www.helpwithwindows.com/WindowsXP/activation.html
make sure to read the link above, and then at the end of the article click on the
"Changes to Windows XP Product Activation in Service Pack 1" link