I have Windows 7 (x86 german) RTM and cannot join my samba pdc domain. Windows 2K and WinXP can join to it w/o problems.
From Win7 I can access the samba-server via \\fileserver. When I click on join domain, I enter the Domain name and then I'm asked for credentials. But then I get the message: "Cannot join domain, it's not existing or it's impossible to connect to it." (my translation of the german message). -> loglevel 50: no log.PCname.logfile exits.
When I use the registry keys (described on http://www.1stbyte.com/2009/05/31/join-windows-7-to-samba-pdc/ and bug #6099 in comment #29, #30 and #31). With these settings the messge "Welcome to domain XX" appears but then in the samba logs the message from bug #6099 in comment #23 appears and on windows I see the message about some error with a broken DNS suffix "" which isn't changeable somehow.
After rebooting win7 i'm in the domain, but cannot login because the trust isn't set up correctly (says windows) and on samba the message from bug #6099 in comment #23 appears again.
Joining the domain requires the two LanManager parameter settings, the message telling the dns suffix is wrong still appears, but after that I can log on with a domain user.