Problems posting to server

i have some asp scripts that i have written on our corporate website but i am having an issue posting data to the server. here is the deal. i am using cdonts.dll so that users can send contact information directly to our email boxes. when running this on xp i have no problems but for some reason when i submit the form to the 2000 server it prompts me for a username and password and domain. can anyone tell me why this is the case?