Get List of Active Directory Users in ASP.Net

I am wanting to make a sign in and out site for reception I have made it so far using C#, I have got the visitor part sorted, however I was wondering if someone could tell me how I could let staff choose there name from a list that has retrieved the names from active directory and then that pulls there name into the SQL Database and then adds a row with there name into as including other columns but I can do the other columns. Thanks :)