It could be because you've done other modifying of the source. Such as adding hotfixes or something. Also, why do people feel the need to post a method and a "guide" for a method that has worked since Win2k SP1? By all means, keep sharing, but the process just doesn't change. I mean, if you want it even easier, open up nLite, tell it the XP source, tell it the service pack file you download, and it does it all for you. THen you make the ISO, and burn it.