Whilst doing research on how to upgrade to another operating system ( Lion ) I came across a mention of booting into safe mode. How does one do that? Also How does one boot from a USB drive? I have formatted a 8Gig USB drive and placed the installer package on it. I just cant get the iMac to boot from it! I am a long time PC user and have just recently migrated to Apple. This is all new to me! Thanks in advance.