Hello,
You mention that you have a Domain in your office... that implies that there is a file server present, and also implies that there is space on the server for you to share files with others at your company. By helping you out here, we might be undermining your IT department's goal of keeping corporate assets (your data) on the server for backup purposes, and avoiding a dangerous peer-to-peer networking.
That said, let's look at the technical answer:
Let's say that you are trying to connect to Brian. Brian is running 2000/XP, and you are trying to connect to him. When Kissy tries to call Brian, it asks for a password. This implies that the network is working, the file shares are properly defined, and file sharing is enabled.
My guess is that the local NTFS permissions on Brian's computer do not recognize you. Typically, we solve that by placing a special group called DOMAIN USERS into a folder on the local computer (Brian) and check the NTFS permissions to allow for sharing. You should also check the File Sharing permissions to make sure you are allowed to connect and read those files (again, making sure that DOMAIN USERS can share).
I would encourge you to talk with your IT department about setting aside file sharing space so that your group of workers can share files in a controlled and safe manor. Remember, if you make that laptop wide open so that everyone can connect to you, and then you dialup somewhere onto the internet, you could be attacked from the internet in short order.
At the last place I worked, we disabled peer - to - peer to have us help users manage their data in a responsible fashion.
Christian