Hi there, just answering my own question after some weeks ;)
I had problems authenticating Windows Vista Internet Explorer clients ("wrong password"). Now I found the "solution" in a note on the module's homepage http://modntlm.sourceforge.net/ I quote it here for the archive, basically it says that the module does not work with NTLMv2 what is used by Vista by default. Jens. Update April 2007 by Michael Baltaks There are two options for NTLM authentication in Apache without using Windows (If you're using Windows, mod_auth_sspi is what you need). The first option is this apache module, mod_ntlm, source code for apache 1.x and apache 2.x. The source code is kept in Subversion, so try svn co https://modntlm.svn.sourceforge.net/svnroot/modntlm/trunk to get it. This includes the improvements from http://modntlm.jamiekerwick.co.uk/ as well as a patch to support reverse proxy mode. This module has no other dependancies, but doesn't support groups or NTLMv2, which is by default the only NTLM allowed in Windows Vista (you can change that setting). The second option is mod_auth_ntlm_winbind, which requires a working winbindd (get some help with winbind). The benefits of bothering to configure winbind are group support and NTLMv2 support. Read about it at http://adldap.sourceforge.net/mod_auth_ntlm_winbind.php.