Much like in previous versions of Windows you can enable an extra level of security by requiring the user to hit CTRL+ALT+DEL before they can enter their username and password. Whether or not this actually makes your system any more secure is up to debate, but if you are looking to enable this feature in Windows 7 by following these steps:

Press the Windows Key and R at the same time to open the Run dialog

Enter “control userpasswords2” and hit OK

In the dialog box select the Advanced tab

Look to the bottom under Secure Logon and check the box beside “Require users to press Ctrl+Alt+Delete”

Click OK

Now when you boot your system users will be required to activate the logon screen by using the three finger solute.