What does IBU mean + warranty enabling?

Well, as the title suggests, I am wondering what IBU means? My XPS laptop has a Dell IBU: Europe. Just wondering what that means. Is my warranty valid only in europe?

Also, do I need to do something to enable my warranty? I see on my system information page as a start date 4/17/2008 and I just bought it a couple of days ago. Does the warranty start when the product if shipped and not when I buy it?

Thanks!