I'm getting a few questions from my post on using the AD Membership provider in ASP.NET 2.0 Beta 2, so I thought I'd share a little more info. Specifically, one of the suggestions from the dev team that was very helpful in overcoming my inexperience with AD was a utility called ldp.exe, which allowed me to verify that I could log into and query the target Active Directory container separate from my application code. It also gave me a good view of some of the connection syntax, which helped me piece together what I was doing wrong. The ldp.exe utility is described in the following KB article
If you're having trouble with coding against AD, it might help you work out where your issues are.