Just a suggestion: You do not need to have them retype this information just for security purposes. If you want to be sure that the users are authenticated as domain users but make it simpler for them to use web access, set the Directory authentication method on the web site to Integrated Windows Authentication. This will authenticate the users, but if they are logged on to their workstations with their network credentials already, they will not have to retype them. The system will see thatthey are already logged on to the domain and bypass the login box. Only if they are not already logged on to the domain will they get the login box and have to fill in the information. This is actually more secure than basic authentication - wherethey have to retype their credentials - because it is encrypted as opposed to having them send their user info in clear text format over the network.
Hope this helps!