remove domain

I'm assuming you are talking about the list shown in the log-on screen.

The domains shown in this list are determined by trust relationships between your domain and those domains.

If you are a domain administrator (and are sure no one else is accessing those domains), you can remove domains from the list by removing the trust relationships with those domains.

If you are a user, sorry, you are stuck with the list as-is, unless you are the only one who was accessing those domains and canconvince your domain administrator to remove the trust relationships with those domains.

The domains visible in Network Neighborhood are displayed due to the Computer Browser service. Now I looked myself to try and purge the Browser lists, but I could not find anyway.
There are ways to verify the Browser information, though. Try Technet article Q188305 for information on the Resource Kit BROWSTAT:
http://support.microsoft.com/search/preview.aspx?scid=kb;en-us;Q188305
(please remove any spaces)

Also, if you have a "phantom domain" on your network for a while, you have to remember that could just be one that is connected to a domain that your domain is trusting. So, you on DOMAINX trusts DOMAINY. Then, a person brings in a laptop that is a member of Workgroup LAPTOP and plugs into and gets an IP address that serves DOMAINY. At that point, the Master Browser in DOMAINY will add LAPTOP as another domain visible. Then, since you trust DOMAINY, the Browser info from them is replicated to your Master Browser.
And therefore, you see LAPTOP as a new domain, eventhough it did not originate in your DOMAINX.

The trick I like is to open up your WINS Server database, Show the database, and sort it by Type. See if you have any 00h, 1Bh and/or 1Ch records (I think 1Ch is the one you want). Find the domain you want to get rid of and select Delete Owner.
The point of this is that you 1) get the IP address from the domain to see if it really should be visible or not to your domain and 2) possibly clear out the reason for the records being propagated to the Browser service. 'Cause this is what happens, is that Browser service gets told what is there, even it it really ISN'T there!

hope this helps