if you already have the gm downloaded for your device just download itunes 10.5 beta 7. If you have edited the hosts file on itunes make sure to delete it before you do anything else. Next just plug your idevice into your computer and put it in dfu mode. Then click shift restore and look for your firmware. Just sit back and let it do the rest on its own. I just installed ios5 gm on mine today with these exact steps. and im not a dev nor is my udid registered!