I installed the forwarder dol by going to "Load/Install File" in priiloader, pressing 2 to delete the current file, then choosing the forwarder and installing it.
I have just done the same but chose the actual USB Loader GX dol instead of the forwarder, but then I get no signal when I boot the wii and I have to go back to priiloader and delete the installed file. I don't know what else I can do in terms of configuring priiloader in order to get it working!
You should be configuring priiloader to run the app directly. Not the forwarder. (I don't use forwarders, since I think they are more trouble than they are worth).
Ok, that clears that up! Now, any idea why I get no signal when booting the app directly? In fact, I think the wii hangs as I gave to hold the power button to turn it off.