How do I backup my complete iTunes library (to new a PC)? I am currently using XP on my laptop, which has the iTunes library. 
I use it to sync my iPod/iPad.

I am planning to buy a new laptop (Windows 7). How do I make the transition seamless to the new iTunes library switch ?
i.e. I should get all the Music/Movies/Apps/Photos,etc on my new Win 7 laptop seamlessly.
Apple has a support document for this: iTunes: How to move your music to a new computer. It also covers things like de-authorizing your old computer from the iTunes Store etc.