You can get them anywhere. Windows will automatically resize them to fit the 32X32 dimension. If you have any sort of screen capture tool you can surf around and get what ever picture/image you want and apply them to the system.
The default size is 48x48 and to appear in the list they should be in C:\Documents and Settings\All Users\Application Data\Microsoft\User Account Pictures. If you don't want to make your own pictures you can find a lot here: http://abc.xplogos.com/.
Ep, glad to see you come back and tidy up...did want to ask a one day favor, I want to enhance my resume , was hoping you could make me administrator for a day, if so, take me right off since I won't be here to do anything, and don't know the slightest about the board, but it would be nice putting "served administrator osnn", if can do, THANKS