the windows server 2003 (or 2000) support tools installation includes "ldp.exe" This allows you to browse the Active Directory (get those DN, DC, and OU's right!) for an LDAP lookup... (or search) ... or Anti-Spam Server Proxy ... ASSP LDAP Login configuration
Double click on LDP.exe
Connection -> Bind ... type in your username,password,domain ... maybe you need to be domain admin?
Should get lots of output ending with "Authenticated as dn:'username'."
View -> Tree (Leave Base DN blank)
Now you can use the + symbols in the left hand pane to browse around your AD