How to get Computer Mack Address

Question

hi everyone,
i start website using vs 2005 C# asp.net. i have to check computer mack address at my login period. i need to check username, password and computer mack address.
i dont use vs 2005 login control. im using my own logincontrol (two textboxes for user name and password).
anyone know how i get computer mack address and check  this using c# coding.
thx