LDAP win authentication problem?

Hi,

I am trying to set up a windows authentication  on my asp.net web application.
I have a security group on active directory which is called, RedTeam and BlueTeam.
I am following this article and I can't make it run.
How to authenticate against the AD by using forms authentication and c# (http://support.microsoft.com/kb/316748)

I am using the exact code in this article.
1) My agency's server name goes like this, myagency.xy.abc.
From my computer, I used nslookup and found something like abc001.myagency.xy.abc.
I guess I am not sure exactly if I got the correct name.

String adPath = "LDAP://myagency.xy.abc"; //Fully-qualified Domain Name


2) It errors out from this line.
Object obj = entry.NativeObject; <===
What does this do? Do I need this?
Without this, it still errors out saying that my userid and/or password are incorrect.

3) Do I use this SAMaccount?
search.Filter = "(SAMAccountName=" + username + ")";
I want to check if this is userid is in AD and my security group (ReadTeam or BlueTeam)

Do I use this instead?
objectClass = User

4) I am testing this from the VS2010 and it is telling me that my userid and/or pw are incorrect.
How can I fix? This should be something easy but I can't make it work.
can you helP?

5) all I want to do is I want to authenticate users against the security group on active directory.
I want to use their windows ID & PW and check it against ldap, if they are in the group, let them access the application.
Thanks