I would love to know it!
What I know is, that *.xp is a certain way to store data just like *.zip or *.rar
Usually there is an encryption used on it - so people like us can't read and modify it.
So to get access to these data you need to know what encryption is used, and use that info to gain access.
That's about what I know of it.. Wish someone who's experienced in this would look further onto this.. But I guess the 9Dragon's section doesn't have such experts :/