Unwanted Domains

I manage a Windows 2003 network for approximately 150 users. At one time we were much larger, with a child domain. That branch has been desolved and the child domain removed according to MS Whitepapers. However, whenever I browse My Network Places, i still see the child domain listed. How do I remove it? Also, when someone plugs a laptop into our network, the machine shows up as a domain\workgroup and stays for a long time. How do i remove them as well?