Forget about an iMac. For uncompressed SD work you need a serious machine. MacPro, MacBook Pro. And they must be running Tiger, as the current version of Avid MC and Mojo do not work with Leopard.
The firewire bus will be tied up with the MOJO, so a firewire drive will not work. Firewire is also not recommended for uncompressed SD work.
An iMac is not the tool for uncompressed work. DV and HDV yes, uncompressed...nope.
Shane
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