Do you have customart enabled in your xstartup.cfg file?
To allow custom art to be used in NBA Live 2003 PC, it needs to be enabled first.
You might want to read thru the
NLSC Customization Guide for NBA Live 2003 for an explanation of the custom art process.
Basically, to enable customart, you need to edit the xstartup.cfg file, using Notepad, and change the last line so it reads "customart 1"
The xstartup.cfg file is normally found in your c:\program files\ea sports\nba live 2003\main\cscripts directory.