Today I found the solution about Leopard needing 3 minutes to log on Active Directory.

It’s due to our AD whose name ends with .local… .local is reserved for the Bonjour services (and AppleTalk).

So I just had to use iServeBox to stop using BONJOUR Daemon.

Thank you little demon :

PS (06/06/2008) : Mac OS 10.5.3 fixes the bug at last !!!!! you can have Bonjour and AD in the same time