I assume that you are asking to hide users in the welcome screen.

To do this, go to this key in regedit
HKEY_LOCAL_MACHINE\Software\Microsoft\WindowsNT\CurrentVersion\Winlogon\SpecialAccounts\UserList

Under this key create a new DWORD value with the name of the user, say Jimmy, and then put decimal value acc to following-
0 - Hides the user from the welcome screen
1 - Show the user in the welcome screen

How to log into the user that is not shown in the welcome screen?
Press ctrl+alt+del twice and then login with the appropriate usename and password.

This trick works only in XP professional.

Another simpler approach is this,
Log in as an administrator and go to Control Panel > Administrator Tools > Computer Management > Users. Now selct the user you want and under the options use the check box to hide or display the account.

But the best option is this,
don't use welcome screen.

As far as I am aware you can't be in the administrators group and not appear when the group is enumerated.

Jimbob

you could sort of hide the admin account by creating a group and giving it the required permissions.  is there something in particular you are trying to achieve or just be a hidden admin?

in that case it might just be easier to know the username/pass of an admin to do your evil bidding

If it's an AD domain you're wanting to do this in could you not set security on an OU to limit read on that, create a new group in it and add your users to that group, and the group to admins?

Might test this out when I get a spare min.

but i want to know how we can enter the server computer without his knowledge?
and can u tell me any thing about wireless hacking???

I can't quite decide whether this is a serious post/request or someone being sarcastic..?

Why do I have a horrible feeling that it's the former