Using Active Directory authentication with Samba on Ubuntu 9.10 server 64bit

The first thing you should do is check your Samba logs, and if need be turn up the log level: http://oreilly.com/catalog/samba/chapter/book/ch04_08.html

Samba is fairly verbose and helpful when it comes to explaining why a connection was not permitted. You'll no doubt find some very good hints as to what your problem is in the logs. e.g. Find the original error message and do a Google search.

When connecting from a windows machine to a share like that you need to specify the domain:

domain\user 

This is only necessary when the windows machine is not joined to the domain.

With regards to you second question, the answer is yes. Example config:

<Location /svn>
DAV svn
SVNParentPath /path/to/svn
AuthType Basic
AuthName "SVN"
AuthBasicProvider ldap
AuthLDAPBindDN "CN=BINDUSER,CN=Users,DC=domain,DC=com"
AuthLDAPBindPassword BINDPASSWORD
AuthLDAPURL "ldap://ldap.server.hostname:389/OU=Users,DC=company,DC=com?sAMAccountName?sub?(objectClass=*)"
AuthzLDAPAuthoritative off
Require valid-user

It's important to note that AD will not allow anonymous binds so you'll need to create a user to bind with. Something like svnauth, and replace BINDUSER/BINDPASSORD above.