You can easily manage that group of pictures:
1. Go to "C:\Documents and Settings\All Users\Application Data\Microsoft\User Account Pictures\Default Pictures" (note "Application Data is a hidden folder)
2. Delete any User Pictures you do not want or use
3. Add in any of your own 48x48 pixel images (bmp, gif, jpg, or png) you want as user pictures.
Now the User Accounts control panel has a much more customized feel to it, and you don't have to fish through all those unwanted images Microsft gave by fefault for your User Picture. This can be good if you want to "brand" your Windows XP system with your images if you build computers.
Note: In Control Panel - User Accounts you can click an account - "Change picture" - "Browse for more pictures" to use any picture you like. It will be converted to a 48x48 bmp automatically.