Hello I need to backup my old imac 17 using the disk utility(I heard you can then boot from the disk on another computer, is this true?) What I want to know is if I make an external HD the destination, will it use all the HD? Because my imac capacity is only 80 GB and the smallest external HD I found was 250. I mean can I use the rest of it for backing other files on my newer leopard system or not? Plus will the backup work with the slower USB, because I can't find smaller HD's with firewire.