Want to change your Windows 7 Logon Screen? First thing you want to do is find a really cool/fun/neat image, I like this one. After you find one you want, go Start (in this case Windows Logo in the lower left hand corner) and type regedit

Once you are there find the key HKLM\Software\Microsoft\Windows\CurrentVersion\Authentication\LogonUI\Background

You will have to add the DWORD Value OEMBackground with a value of 1
Be careful not to have any extra spaces if you are cut and pasting OEMBackground to the value name or it wont work

After that, go to start and type C:\Windows\System32\oobe\ and add the folder Info, then inside of Info add the folder Backgrounds

Once you have the backgrounds folder you want to  copy your image there with the name of backgroundDefault and make sure it is a jpg file
Also note, that if the image size is over 256K it wont display

If you did it right, when you lock your workstation (winkey+L) you will see the image

Also there are some other values you can play with, in the HKLM\Software\Microsoft\Windows\CurrentVersion\Authentication\LogonUI folder you can add the DWORD value of ButtonSet with a value of 1 or 2
1 = Darker Text Shadows and button colors
2 = No Shadows and no transparent buttons