I probably can't help to much, but I can get you off in the right direction I think. LOL, ah well here goes:
Have you added the Microsoft Identity Management for Unix Role Service to AD? If not do so.
I joined Ubuntu to my AD domain 2008R2 Server using likewise-open using ADS security settings. I saw the ldap selection in the drop down of available authentication types but I did not use it, I selected ADS instead (Active Directory Services).
I don't use RH. I did try the following with Fedora 16 and it did not work out perfectly. I did also do the following with Ubuntu 10.04 LTS and it worked perfectly.
installed likewise open and samba-winbind apt-get in ubuntu and yum in fedora.
After that I used the likewise open shortcut I found in the administration menu's of each OS and from there it is pretty self explanatory, plug in DC and REALM, select security type and click join button. As I said, I never did get it working right on Fedora 16 (64 bit) but Ubuntu 10.04 LTS did it all seamlessly.
On the Windows 2008 server side, after you install Mgmnt for Srvs for unix, create a (global/security-defaults) group and use the groups properties sheet to configure the unix attributes. You can also do the same for each unix user you create. I am also just learning Windows 2008 Server. I have had some previous experience with 2ksrv and various versions of linux.
I found it easier, being gui driven, to find the GUID of the user on Ubuntu. I still haven't figured out how to find it on Fedora. I forgot how to do it and have had time to google it yet:-)