sure,
basically, you need to connect to the ldap server specifying the username and password in the ldap "url" . in the end you are going to run the FindOne() method on your ldap connection object with arguments that specify a uid and a passwd. Then you compare whether the FindOne() method returned null (in which case the user was NOT authenticated).
I found two pages on the web that talk about authenticating against LDAP servers. They don't talk exactly about domino ldap, but they talk about active directory (microsoft's ldap server) and sun ldap. I'm sure you could probably use the same code or modified just a little bit because sometimes ldap implementations are different between servers.
the first one talks about how to do authentication against active directory (which is nothing but windows own ldap server) you find it here
http://www.codeproject.com/aspnet/ac...rectoryuse.asp
the second one talks about authenticating against sun ldap server, you find it here
http://www.experts-exchange.com/Prog...estCookie=true
(you might need to subscribe to the site to view the solution)
hope that helps