First of all the best way to do that and teh standard way .
Is to make use of teh free tool logon studio.
Load the .logonxp files and apply them and it is done.
You can make your own custom logons, just open the .logonxp files and learn how teh resources are structered ni it.
But anyway if you want to hack it yourself, instead of just customize it.
Then this is the way i do that.
1-Go to c:/windows/system32
2-Backup the file logonui.exe
3-Open a copy of the file with resource hacker (this is a free utility).
4-Go along all the resources stored in teh .exe file and change them to your own custom graphics.
5-Restart your computer in safe mode, an duse teh command line to overwrite the new custom logonui.exe over the old one.
6-Restart your computer again in normal mode.
There you go, the logon is changed just like zouzou.rocket has said.
Easy as cheesy, it is difficult only when we do not know things.
zouzou.rocket
Rocking teh house