Although 9.04 Jaunty Jackalope has improved its hardware support overall, many users are reporting problems with getting their wireless adapters to work correctly after a clean install of 9.04 despite wireless working out of the box on previous releases of Ubuntu. In most cases the adapter is detected and can be seen in the NetworkManager Applet in GNOME, but no wireless networks appear.
I had this problem while installing Ubuntu on my Evo N610c. The wireless PCMCIA card I am using is a WPC54G (revision 1). I also tried a Netgear MA401 and a 3COM 3CRWE73796B wireless B cards as well. All had the same problems, and all worked when I previously have used 8.04 or 8.10 of Ubuntu or Xubuntu. I also found I had the same problem with my work laptop, a Dell C600.
After a little bit of research online I noticed that this was a common problem, and many people were having trouble getting their wireless to work with 9.04. It seemed to be a common problem, esecially with people using Broadcom wireless adapters.
What was needed is to use the proprietary drivers for the Broadcom wireless cards. This can be done by going under System -> Administration -> Hardware Drivers and enabling the Broadcom B43 Legacy Driver. When I first went here after a clean installation, there were no drivers listed however.
I ended up getting the driver to appear under Hardware Drivers by updating the system, updating APT, and updating Synaptic. Whether doing all of this may not be necessary, once completed the Broadcom B43 Legacy Driver appeared under Hardware Drivers. To do all of these, do the following bellow. you will likely need to connect your computer to the internet using ethernet unless you have another wireless card that is working.
Update the System:
Open System -> Administration -> Update Manager
Update Apt:
Open the terminal then type in: sudo apt-get update
Update Synaptic:
Open System -> Administration -> Synaptic Package Manager then click "Reload" in the upper-right coner.