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

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.