This is pretty easy using the Ubuntu restricted drivers tools: Ubuntu Menu -> System -> Hardware Drivers (in the 2nd box of applications). Note that you’ll need an Internet connection to actually install this so hopefully you can make use of a wired connection temporarily! When I initially installed this driver there were actually two to choose from but it was the Broadcom STA driver that worked. Now I only see a single option available.

Creating the indicator
The class used to represent an indicator appears to have changed from IndicatorMessage to Indicator so I threw in the following code to try the new one and fallback to the old one:

try:
  # Ubuntu 9.10 and above
  indicator = indicate.Indicator()
except:
  # Ubuntu 9.04
  indicator = indicate.IndicatorMessage()

Drawing attention
Previously, indicators automatically made the indicator applet draw your attention with a green dot. In Karmic the green dot appears to have been replaced with a change of the envelope colour to black but it is no longer automatic. To make this work you need to set the draw-attention property:

indicator.set_property('draw-attention', 'true');

Note that they’ve also added a count property to display how many notifications are from the same source.