BYPASS AUTOLOGON
This Registry tweak works with all Windows NT 4.0, 2000 and XP releases.
If you own the Windows computer, have Administrator privileges, work/play in a single-user/stand-alone environment, and would like to speed up the bootup process, you can automate the way the OS handles the password dialog box, bypassing the mandatory Ctrl-Alt-Del login prompt.
CAUTION: This will affect system security, leaving your computer unprotected!
Start by BACKING UP your Registry files!
Then run Regedit and go to:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
In the right hand pane look for the "AutoAdminLogon", "AutoLogonCount" {DWORD [REG_DWORD] Value}, "DefaultDomainName", "DefaultUserName" and "DefaultPassword" String [REG_SZ] Values.
Highlight "AutoAdminLogon" -> right-click on it -> select Modify -> change its value to 1 -> click OK.
Highlight "AutoLogonCount" -> right-click on it -> select Modify -> check the Decimal box -> change its value to 4294967295 (maximum allowed) -> click OK. This is MANDATORY to be able to take advantage of the auto login feature more than once. [4294967295 times should be plenty.

]
Now highlight "DefaultUserName" -> right-click on it -> select Modify -> change the text to match your UserName (default is "Administrator" if you haven't changed it) -> click OK.
Repeat same steps for "DefaultPassword". [Choose your Password wisely!

]
If you are not logging into or do not have a (Network) Domain account, you can leave the "DefaultDomainName" String Value empty, or delete it altogether.
If any of these Strings do not exist, you need to create them: right-click on an empty spot in the Regedit right hand pane -> select New -> String or DWORD Value -> assign it one of the names above -> press Enter -> right-click on it -> type in the appropriate text string (as described above) -> click OK -> restart Windows when done.
If you are unwilling to "mess" with your Registry, you can also achieve this by using one of these Registry tweaking tools:
ALL WinNT4/2000/XP users: log on as Administrator -> click Start -> Run... -> type (case insensitive):
control userpasswords2
Hit Enter or click OK -> make sure there is NO check mark beside Users -> enter the User Name and Password you wish -> click Apply/OK/Yes until all following dialog boxes are closed -> restart Windows.
ALL WinNT4/2000/XP users: get XQ|DC X-Setup Pro 6.6, the best Registry and System tweaker ever created [freeware for personal use].
Install X-Setup -> start the main UI -> Network -> Auto Login -> Windows NT/2K/XP -> General + Settings plug-ins -> enable/fill in all appropriate Auto login boxes -> Apply changes -> close X-Setup -> restart Windows.
WinNT4/2000 users ONLY: get the MS TweakUI Power Toy for Windows 9x/NT4/2000/ME + MS IE 4/5/6 [110 KB, free, unsupported].
Run the executable you downloaded from URL above -> right-click on TweakUI.inf in Windows Explorer -> select Install -> open Control Panel -> select TweakUI -> click the Logon tab -> check the "Log on automatically at system startup" box -> type a User Name and a Password -> click OK/Apply -> close TweakUI -> restart Windows.
WinXP users ONLY: get the MS TweakUI Power Toy for Windows XP + MS IE 6 [147 KB, free, unsupported].
Install TweakUI by running the executable you downloaded from URL above -> run TweakUI -> scroll down to the Logon section -> set the default User Name and Password you want to use -> click OK/Apply -> close TweakUI -> restart Windows.
Optionally, if you need to log on into a NetWare Domain/Network, go to (using Regedit):
HKEY_LOCAL_MACHINE\Software\Novell\NWGINA\Login
In the right hand pane look for the "NetWareAutoAdminLogon", "DefaultNetWareUserName" and "DefaultNetWarePassword" String Values.
Repeat the same operations above for these entries: type 1 in the "NetWareAutoAdminLogon" box, and respectively your NetWare UserName and Password. Restart Windows when done.
BEWARE that all these Password strings are kept in the Registry as plain text: unencrypted! Therefore anybody with access to your computer, who knows how to change the Registry [this includes you now

], CAN alter/delete them at will!
UPDATE: "There is another way to accomplish the same task without modifying the Registry: Start menu -> Settings -> Control Panel -> Users and Passwords. Here you will find the "Users must enter a user name and password to use this computer" option. When this is checked the user must enter a user name and password every time to access the computer. If unchecked the user will be required to enter a user name and password only once after which the computer will use this as the default and automatically log on for you."
[Thank you Al!]