You can make your account have the Vista Inspirat theme (the Black Vista theme), and have the other users use the original XP theme (blue). But, the icons will still change..
If you want to get the old XP logon, do this:
Go to C:\WINDOWS\BricoPacks\SysFiles
Copy the 78_logonui.exe file and paste it on the desktop.
Change the name of 78_logonui.exe to logonuiorig.exe.
Copy logonuiorig.exe from the desktop to the C:\WINDOWS\system32 folder.
Now download the file below, and double-click it. Then press Yes. Now you should have the original logon.
If you face problems, please tell me 
DOWNLOAD PATCH: http://www.zshare.net/download/14557968c09592fd/