Question:  A frequently asked question by Multi-national Administrators is where could I get the MUI packages for Windows XP Service Pack 3?

Answer:  You should use the same MUI package for Windows XP Service Pack 2 and install the following additional item:

942766 An update is available for the Multilingual User Interface Pack for Windows XP Service Pack 3, for SP3 for WEPOS and for SP3 for WinFLP
http://support.microsoft.com/?id=942766

which has a link to the package below

Windows XP Service Pack 3 MUI Pack Update
http://www.microsoft.com/downloads/details.aspx?familyid=D3F8F6AB-84F1-4095-8709-DF509B1BEE22&displaylang=en