[davebarnes]

You need to have a FireWire connection in order to boot from the drive.
You can not boot using USB.
I think you will find that the Seagate model (750GB, $199) you referenced is not FireWire. The model you want is "Seagate FreeAgent Pro ST307504FPA1E3-RK" and the "E3" is very important. NewEgg wants $245 USD.
If it is, then great.

What I can attest to is that OWC makes Mac products that work. Not doubts, no questions, no concerns. I have had excellent experience with OWC and their support. MacSales.com has the "OWC Mercury Elite-AL Pro 'Quad Interface'
FireWire 800/400 + USB2 2.0 + eSATA" 750GB drive for $320 USD.

Me, personally, I would spend the extra $75.