both are possible ofcourse
lets take it step by step shall we ?
theres a program called viewxpkey
google it
it shows ur xp cd key
and even MIRCOSOFT allows u to change ur cd key !! it just requires a lil registry tip

..
there is a software that does this too .. but i dunno if that software is illegal or not so i cant post the name
this is how u do it
Log in Administrator ( to be able to edit registry )
Click Start > Run > Regedit
Go to HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\wpaevents
In the right pane, right-click OOBETimer, and then click Modify
Change at least one digit of this value to deactivate Windows
Click OK and close regedit
Click Start > Run and type in: "%systemroot%\system32\oobe\msoobe.exe /a"
Click Yes, I want to telephone a customer service representative to activate Windows, and then click Next
Click Change Product Key (at the bottom)
Enter your valid Corporate Product Key
Press Update and close the window.
If you are returned to the previous window, click Remind me later
Restart your computer
Source : Microsoft ( i remember seein it there )
i DONT think this is illegal as it solely depends on HOW u use this info. !