I purchased an iMac 20" computer. The previous owner (deceased) formated the hard drive and installed Windows 7 ONLY. I researched and found out I the computer can handle Snow Lepard, but it needs to be installed from OS X. If i purchase the Full Install of Tiger (the original OS), how do I go about installing it? Do I format the hard drive form Windows 7? Not sure what to do. Afraid to do anything for fear of destroying it completely. Thanks.