In Windows 2000/XP you have the ability to disable NetBIOS over TCP/IP.
1. You do this by right-clicking on My Network Places and selecting Properties.
2. Then right-click on the appropriate Local Area Connection icon, and select Properties.
3. Next, click on Internet Protocol (TCP/IP) and Properties.
4. Now click Advanced, and select the WINS tab.
5. There you can disable NetBIOS over TCP/IP.
The changes take effect immediately without rebooting the system.