Update: The Nexus S skin is available at here.
Installation is easy. Just extract it to
<android-sdk-install-root>/platforms/<your-platform>/skins and then use it.
The result is pretty nice
What I forgot to mention. If you have problems with the size of the emulator that is going to be started, you may want to add a
-scale to your emulator run arguments. In Eclipse you add it under your Run Configurations: