Advice please about how best to go about transferring the contents of one external hard drive to another.

Setup:
Mac Mini 2.4 computer
ICZ external enclosure with Seagate 250 Gb drive
Mercury Elite external enclosure with Hitachi 1 Tb drive - both new.

The ME is connected to the Mini via FW800, but I can use eSATA or USB if necessary.
The ICZ has FW400 and USB connectivity.

I need to transfer the entire contents of the Seagate to the Hitachi before sorting and editing. The ICZ/Seagate will then be set aside (for now).

Both Seagate and Hitachi drives are SATA, but I have five spare ATA drives which I connect with a USB/ATA adaptor. Am I right in thinking that an IDE drive will not work inside the ICZ enclosure, assuming it has a SATA connector?

Thank you ..... hugh

PS. if it's of any consequence, I use iBackup weekly to back up the Mini to the Seagate. I don't wish to use Time Machine.