I should have read a little more about the product. It says this at the bottom of the page.
"External video with a Apple MacBooks Pro:
Work with MacBook Pro 2.33GHz only. Use the Nvidia 7300GT graphcis card (Apple part number 661-3932, available at www.mac-pro.com. The ATI Radeon x1900XT and Nvidia Quadro FX 4500 are "double-wide" cards and will not physically fit into Magma ExpressBox1 ."-Magma
Although if the only reason for there being a compatibility issue is size related then you might be able to use a video card of the same size..