However, it turns out that this is probably not a sample of Atta's handwriting. First of all, there were 3 of these documents; according to a newspaper article, these 3 were similar but not identical; I don't know which of these 3 is pictured in the FBI page above -- it doesn't seem to say (the FBI page implies that the 3 are identical).
The newspaper article also gives an analysis of one of the writings (Alhazmi's). What the article says is quite surprising -- I'll find it and post it also. Supposedly these writings were dictated to a woman by either a non-native speaker of Arabic or an uneducated Arab. They're said to be confused in nature, not exactly suicide notes or instructions for terrorists; it's not clear what they are.