Can Keyloggers get passwords from Windows 7/8 Logon Screen?

The log on screen is created by the WinLogin process. If a program can bind to the WinLogon process then it can most definitely keylog your login password.

The Metapreter Payload from the MetaSploit library is a good example of a tool capable of migrating into the logon process. You may look at "MetaSploit Unleashed", to learn how to compile Metapreter into a binary payload (.exe) or attach that to another (.exe) and obtain the same results.

A good demonstration of the technique can be seen at : Clicky

More References:

• http://www.offensive-security.com/metasploit-unleashed/Backdooring_EXE_Files

• http://www.offensive-security.com/metasploit-unleashed/Existing_Scripts

Note: Use of any kind of malware or spyware should only be done with prior consent of the system owner and/or users.

Also, look at Polynomial's comment below for other ways. +1 to him ;)