Hi Robert and welcome to the forum!
This is probably the most common question. We provide the Active Directory Web service for $19.95 that does this for you. Check out the Premium Downloads section of the forum for a couple HowTos that explain how easy it is to use.
Another option is to use Environment.System.Username but that just gives you the alias of the user. For the full name you need the Active Directory Web service.
Good luck!
Patrick Halstead
Project Manager at Qdabra