How do I remove domains from the network browser?
When this periodically happened to me, it had to do with permissions being incorrect in the following areas, preventing me from making changes:

In Snow Leopard (10.6) and later


Open ~/Library/Preferences/com.apple.sidebarlists.plist in a plist editor
Find the section favoriteservers
Remove listings for those stubborn locations


In Tiger (10.5) and earlier (if I remember correctly)


Navigate to ~/Library/Favorites
Add/Remove the files with the pesky server names


Hope this helps