Apply theme silently ?

Hello,
How can i change an xp theme or style silently without confirming the dialog wich appears when clic on a theme file, most programs like Tuneup and Auslogics Visual Styler uses rundll32.exe process to run a function from a DLL ( dont know wich one ) probably shell32.dll, user32.dll or themeui.dll . so i need these parameters or an utility to show them.