Sorry, but there's no way that card is gonna work in that Mac.
There's a whole list of reasons why, not the least of which is that the card you have is PCI card and you're Mac Pro has PCIe slots. PCIe is two generations ahead of PCI.
To see what kind of stuff we (I'm the Product Manager for Media 100 these days) offer that WILL run in the Mac Pro, start at
http://www.media100.com and give our sales dept a call.
~ Wick