Hi and :welcome
Unfortunately Eyefinity does not span multiple cards, it can only use the outputs from a single card, but can use addtional cards for extra horsepower by enabling CrossFireX.
To achieve 5 displays you would need either the 5870e6 or a 7970 Flex 6G (due date unknown).
Alternatively you could use a Matrox Dual/Tripple Head2Go along side any ATI 5xxx series or above card with the 12.2 drivers to gain support for Eyefinity 2.0 which allows you to have different resolutions and bezel compensations, to split one of the DVI or DP outputs to 2 or 3 of the monitors.