Hello everyone. I'm trying to flash my ATI HD5770. I read up and did some research and I think I can pull it off. However I have a (probably) very stupid problem. I have the HD 5770 plugged in on my Mac Pro 2008 as I type this so I can't log in OSX of course and I can't access the boot option by holding the command key. I have bootcamp booting my Windows partition automatically. My question is how do I get it to boot from the usb pen? I have the USB pen ready and it should be bootable but where can I set it to look for the pen before accessing the Windows partition? Thank you!!