Howtoforge posted a tutorial about changing the desktop appearance on Linux Mint 11

This tutorial is supposed to show you how to change the GNOME desktop appearance on Linux Mint 11 further than the standard options of the Appearance section in the Control Center allow. I am going to use several different applications for this cause. This is the standard desktop that comes with Mint, so if you have not changed anything about that all steps should work fine for you. Be aware that the use of the nVidia proprietary drivers may not be unrisky!

  Changing Desktop Appearance On Linux Mint 11 (Advanced)