Not sure what you've tried, but I have Belkin Wireless G USB F5D7050 installed on an old Dell Latitiude CP M233St with xubuntu and a Desktop running ubuntu hardy herron. Responding on Desktop using Belkin F5D7050, v. 3000 with rt73 driver. Install has been the same using ndiswrapper and the Belkin install cd as follows: (This process should also work for your USB)
Unplug adapter before you boot.
Install ndiswrapper through Synaptic.
Remove the following drivers using these commands:
sudo modprobe -r rt2500usb
sudo modprobe -r rt73usb
I'm not sure that this actually removes the drivers, but after 3 weeks of farting around with them it made me feel better.
Blacklist rt2500usb and rt73usb by opening text editor (mousepad for Xubuntu - gedit for Ubuntu) as follows:
add "blacklist rt2500usb" and "blacklist rt73usb" (Without the quotes) to end of list, save and close.
sudo gedit /etc/modprobe.d/blacklist
This is where the guides I was following failed. Blacklist doesn't work until you reboot. If you don't, the wrong driver will be associated.
On your desktop, open "Home" - right click in an open area and create a file - I called mine "Belkin". Insert the install cd. Open and navigate to the driver file under XP. there will be 3 files. Copy all 3 files to the file you created under "Home" by dragging and dropping. The drivers will not load directly from the cd.
Now install the driver you just copied with the following (If the .inf file you copied is not the rt73, replace as appropriate below) :
Insert the wireless adapter.
sudo ndiswrapper -i /home/(your user name)/Belkin/rt73.inf
Now issue the following commands:
I think these create the module. Now edit modules to load ndiswrapper when you boot as follows (If you are using Xubuntu, replace gedit with mousepad):
sudo depmod -a
sudo modprobe ndiswrapper
Add "ndiswrapper" (without quotes) to the end of the list.
sudo gedit /etc/modules
Establish alias with following command:
sudo ndiswrapper -m
Give it a shot.