Absolutely not and I don't believe it is a sin either.
I think few people believe this these days.
Really? Its the ultimate act of selfishness and trying to destroy God's will. Its a sin but I'm not sure if it ends in eternal seperation from God.
I really don't think suicide is the "ultimate" act of selfishness.
Those that committ suicide are not stable. I don't believe (and neither does the Church, by the way) that God punishes those that aren't able to think rationally.
So what about the 9/11 hijackers?
What about them? Are you really asking if I think that their suicide was justified? It doesn't compare, dope. Their suicide isn't simply excused since they were responsible for the deaths of thousands of innocent people. It's not simply a suicide.
Then again, I'm not in God's position to say whether or not they're truly sorry for their sin. I do have a feeling that with their warped, murderous thinking that they aren't in heaven...