how about replacing the hard drive with a solid state drive SSD, and trying to put that in the same location? Maybe remove the optical? I am afraid you are going to have to remove something to be able to make it work...
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"Fix it 'til it Breaks."

Jacob - EiC & Director of Technology
Mac Pro Quad 2.66 - 4GB RAM
160 GB SATA RAID 1 - 650 GB Storage
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Accessorized to the Hilt