If i'm not mistaken the "slmgr" steps are done when you inadvertantly use an Upgrade DVD to perform a Clean Installation that creates a problem with activating your product key.
But if it's already succesfully installed and activated into one of your computers the slmgr fix won't work. The easiest suggestion is to give MS a quick call and tell them of the change in computers and they will use another tool to reactivate your product key
When you activate, it ties the key to the hardware config (given in tut. linked below, scroll down) until another key claims that hardware config.
That's why even if you format over your XP, it will still require a robocall to reactivate, trading a series of numbers which deactivate the key on the old machine and activate the new one.
Vista and Win7 apparently can accomplish this using internet activation.
You will get activation on a retail key as long as you aren't trying on more than one computer at a time. You own the key for life. MS cannot steal it back.
The only time I tried to remove key using slmgr command in Win7 I got "Windows not genuine" but was able to SysRestore.
http://www.pcbuyerbeware.co.uk/ProductActivation.htm
Others experience?
Quote