I have a legit version of windows after running copied for ages.
There is a line of code you can enter into the URL when visiting the update site and it'll bypass the Windows Genuine Advantage thing. Once that is installed on the pc though I don't think you can get past it, though I'm probably wrong. My way, you install XP pre sp1, install sp1, use the code, then it lets you install sp2 and all other updates.