XP-tan is a phenomenom which happened only with the help of macromedia flash and a screencap. there are two HQ-Vids of it. There's NO PROGRAM for xp-tan! Need's to be written if you'd ask me =)
More material (everything existing): Windows XP - Boing Edition http://youtube.com/watch?v=QiOVwWxWQ-0
Hopefully, someone will write a software for Windows like that...
A translation of what she's saying in this flash:
Windows Xp has started. You're up early today..~nee? I'm happy! It might not be much but I am able to see you a little longer than usual.. HeHe