Official instructions are here, but this method worked for me:

install these packages with synaptic:

swig
python-wxgtk2.8
libois-dev
libode-dev
libogre-dev ( Must be version1.4.9 )
libfltk1.1-dev
libxml2
libxml2-dev
scons
libboost-dev
libboost-signals-dev
libboost-signals1.40-dev
openal
libavformat
libtool
libxft-dev

download and install these packages:

wget http://launchpadlibrarian.net/16469340/libogremain-1.4.9_1.4.9.dfsg1-1_i386.deb
wget http://launchpadlibrarian.net/16469345/libogre-dev_1.4.9.dfsg1-1_all.deb

I got the above packages from here:

https://launchpad.net/ubuntu/intrepid/i386/libogremain-1.4.9/1.4.9.dfsg1-1

https://launchpad.net/ubuntu/karmic/i386/libogre-dev/1.4.9.dfsg1-1

modify some source:

cd gazebo-0.8.0
vi server/gui/StatusBar.cc

change:

#include <stdio.h>   // change this
#include <cstring>    //  to this

run these commands (each line by itself), better yet append them to the end of ~/.bashrc to make it permanent:
For Bash: .bashrc (executed when you shart a shell) OR .bash_profile (executed when you log in)
For csh and tcsh: .cshrc
For sh and ksh: .profile

export PATH=/usr/local/bin:$PATH
export CPATH=/usr/local/include:$CPATH
export LIBRARY_PATH=/usr/local/lib:$LIBRARY_PATH
export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig:$PKG_CONFIG_PATH
export LD_LIBRARY_PATH=/usr/local/lib:$LD_LIBRARY_PATH

build the source

sudo scons install

test that it worked:

gazebo worlds/simpleshapes.world

A Note on creating the ~/.gazeborc file: http://www.mail-archive.com/playerstage-gazebo@lists.sourceforge.net/msg00851.html