I read in the newspaper (here in The Netherlands) that an arab journalist working for an English newspaper has interviewed Bin Laden in the past and has good contacts within Bin Ladens organisation. This man told that the artical you're refferring to is correct and that Bin Laden has said more of these things, kinds of warnings or so.

I also read about a former 'employee' of Bin Laden is in America to testify about the attacks on the US Ambassies (spelling) in Africa; this guy told that Bin Laden isn't doing this alone but with the help of the Taliban and other terrorist groups.