Even though it's a cybersquatting name, I think we can be reasonably sure he won't try to sue you for it _\|/_
As far as which is his 'real name', Osama or Usama, in Canada and the US it's been spelled Osama. Not that this makes it his real name, just that this spelling is the more valuable since it gets all the monthly searches ( Osama B.L. gets 368,000 searches, Usama B.L. gets 18,100).
All that being said, I'd still value this as low value unless you luck into some buyer who really wants to create a site around the name and can't afford the dot.com.
I agree with Bannen; the right spelling is Osama. I am really surprised to see that US official sites spell it with 'U'.
As far as the name is concerned, it's worthless regardless of the extension for the fact that the last part is very specific and finding any other Osama whose father or ancestor's name is Laden would be very difficult.
If it is Osama.com it would be very valuable, as it is a common name in the Muslim communities.
I think the us govt is interested in an OsamaBinLaden Net. They've tried other means to catch him and been unsuccessful... a net specifically created to catch him would be incredibly valuable, like a butterfly net is valuable to a lepidopterist...