Here are a few links that helped me out when I first dove into working with AD...

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnpag2/html/paght000026.asp 

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/sds/sds/active_directory_authentication_from_asp__net.asp (C# example but you'll get a good point of reference to start with)

http://www.15seconds.com/issue/060525.htm

If after going through those you have any questions, let me know, I may be able to save you some time troubleshooting.