Okay so I have an Intel Mac running 10.4.11 at the moment (Was on snow leopard but when I clean installed my Mac a few weeks ago I put in the original disc rather than my snow leopard one, which I now can't find for the life of me!) I've got a disc image of Snow Leopard now and have been writing it to a USB to try and boot it from that using disc utility but the USB doesn't come up at start up menu from holding the option key. I've followed the online guides to the letter and have formatted to Mac OS Extended (Journaled) and using GUID Partition Table and then restored the disc image to the USB but still no luck. Not sure what I'm doing wrong. Any help would be much appreciated. Thanks!