Most likely the extra additions the 99asterisk will make won't be possible in AD indeed. Microsoft has Office Communicator that sort of does this function, thus they don't put in those functions. It might be possible to add the ldif though, AD won't fetch those items, but as long as LDAP keeps them it should not be a problem, i dont know if custom made items can be added to users though :p
Currently i can confirm the 99asterisk.ldif works properly, and along with the other edits to the config files you can make asterisk connect to the LDAP server. Softphones work flawlessly, though hardphones might have problems with it for some reason (i think it has to do with DNS).
I think by tomorrow i'm gonna need to make an AD bind to the LDAP too :)
(the funny part is that i am competing with another "stagiaire" here at my work, and he is working with Microsoft Office Communicator vs my Asterisk XD good thing that i am in the lead)