install 2 video card

Hi all, I'm not sure this room is the right one to post this but I've been a fcp user since 2004 and so...I hope someone can help me.

I got an apple macpro 2009 with nvidia 8800 and I'd like to install a used nvidia gtx285: can I install it with the 8800 or I have to remove the 8800 and install the gtx285.
My intention would be to use the old 8800 to run my dual display monitor setup and the gtx285 for the calculation (davinci, mercury engine and so on..): would it be possible/recommendable?

Thanks for the help and sorry again

Tommaso

Thanks Shane,
and so if I remove the old card and install the gtx285 i will avoid problems, am I correct?

Great! thanks again