Before I upgrade to Leopard, a question
 

I have an intel iMac that I will soon be upgrading to Leopard. I have an external USB hard drive with a SD clone of Tiger on it. It is bootable, I have checked to make sure it works.
I noticed in Disk Utility that the external drive is partitioned with Apple Partition Map. Should I erase the drive and repartition it GUID then make a new Tiger clone? I am going to try to do an upgrade first but if it fails and I need to do an erase and install can I use migration assistant with the USB drive to move my user stuff over? I don't have a firewire drive.

In general, APM will work, but if you have the time, I'd use GUID.

I think Migration Assistant will work with a USB drive as long as you point to it with the "volume attached to this Mac" option.