Link to http://teavuihuang.com/android/ and select the skin you like.
Download the .zip and unpack it to android sdk skin folder. e.g. C:\android-sdk-windows-1.0_r1\tools\lib\images\skins.
start the emulator with parameter '-skin'. e.g. emulator -skin HVGA-P-G1.
HVGA-P-G1 is unpacked folder name.