Moving to a new iMac

[DHH]

I am writing to you from Moscow, Russia. Next week I am returning to the U.S. and settling there. In the process of this move I am selling my current 2 year old iMac (250 GB hard drive) and it will be picked up tomorrow.

I have already ordered an brand new iMac 500 GB hard drive and it should be waiting at my new apartment when I arrive.

Currently I have a 250 GB hard drive hooked up to my old iMac via firewire.

This external hard drive has been partitioned to allow for both Time Machine and a sandbox bootable.

I want to use the external hard drive to move the entire contents of my old iMac’s hard drive to the U.S. so that I can load it into the new iMac and continue using my entire setup like normal.

What steps do you recommend I take to copy my internal hard drive to the external drive?

What steps do I take to transfer the contents of the external hard drive to my new iMac?

Additionally an update to the Leopard operating system will be released any day.

If the new iMac I receive from the Apple store has the newer Leopard system and my external hard drive carries the old operating system what problems could this create for me?

Thanks for the help.