Click Start, All Programs, find and right-click the Windows Media Center icon, and then choose Properties. Place your cursor at the end of the Target field, where you'll see this line: %windir%\ehome\ehshell.exe. Now it's time to tack on one or more of the following switches:

/nostartupanimation disables the startup animation so you get into WMC a few seconds faster.

/playallmusic immediately plays your music library.

/playfavmusic immediately plays your music favorites.

/playslideshow immediately plays a slideshow of all your photos.