Three monitor setup and Driver help

Hi guys, I’m not too great with Linux so please try to keep your responses simple and keep in mind that this is maybe the 5th time I have ever used Linux.

I have a three monitor setup with 2 GPU’s. A Radeon HD4870 as my primary and a Radeon 4350 as my secondary. The 4870 has a 24" widescreen monitor and a 17" monitor and the 4350 also has a 17" monitor connected.

I want to have a three screen setup , I got a dualview setup at the moment which is working great but I would like to make use of my 3rd monitor. And also would like to make use of the 3D desktop effects but I think my HD4870 driver is not installed as when I try to enable the option both my screens turn white then after 15 or so seconds revert back to normal.

Please help, thanks in advance!