Open the Start menu and in the search box type
secpol.msc; press Enter to open the Local Security Policy editor. On
the left, expand the branches to Local Policies\Security Options. Then,
on the right, double-click the Interactive logon: Do not display last
user name option, select Enabled, and click OK.
If you’re using the Home Basic/Premium edition of
Vista and don’t have the secpol.msc file, don’t fret. Just open the
Registry Editor and expand the branches to
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\
CurrentVersion\Policies\System.
Double-click the DontDisplayLastUsername value in the right-hand pane
and type 1 into the value data field. If the value is not there,
right-click an empty area of the right pane, select New and then DWORD
(32-bit) Value, and then type DontDisplayLastUsername for the name of
the new value. (It should, but doesn’t, go without saying that you
should back up your Registry before making any changes to it: see
go.pcmag.com/saferegedit for instructions on safely editing the Windows
Registry.)