I personally prefer the OpenSolaris look for Gnome because it`s more clearly then Ubuntu`s Humanlooks. It`s possible to install this theme under almost any system running Gnome.
The easiest way is installing the proper package from gnome-look.org This site contains the packs for Ubuntu 8.04, 8.10 and Debian (both x86 and x86_64).
Another way is compiling and installing the latest version. This is how it goes!
Install the proper requirements and the source;
apt-get -y install build-essential libgtk2.0-dev intltool icon-naming-utils fakeroot devscripts debhelper
tar -xf nimbus-0.1.7.tar.bz2
Next step; compiling the source
chmod +x debian/rules
Install the binary;
make clean make
sudo make install
Select the theme in Gnome.