It's certainly not a current feature of the program. I suppose if you are a database guru you might be able to mod the program to give you the results you need, but every discussion I've seen on the topic has not revealed an answer to this issue. There is no evidence that I have seen that would indicate that the information is even recorded by the database, but again I don't know for certain wether or not that is the case.
I'm not all that familiar with using LDAP but the note within Subsonic states that Users are authenticated by the LDAP server. When the LDAP enabled users log on to Subsonic, the username and password are checked by the external server, not by Subsonic itself.
Therefore, I would think it may actually be easier for an IT expert to get this information from the LDAP server as I would think that each authentication request event would be recorded in the LDAP server logs. You stated that your IS dept requires a way of recording all logon attempts in order to use LDAP authentication. Does that mean that all the other applications on your network have that capability? Interesting issue, but my guess is that it would be easier to get that info on the LDAP end.
Some of this may be relevant or give someone else a few ideas:
http://technet.microsoft.com/en-us/libr ... 80(v=WS.10).aspx
Here's some ideas relevant to Windows 7:
http://answers.microsoft.com/en-us/wind ... a9360efdbf