I just bought a Dell Inspiron 580 running Windows 7 (64 bit). I have an ATI based Radeon HD 4670 video card in the PCI Express slot. I want to add another video card in order to have a third and fourth monitor, but I only have a PCI slot and a PCI Express X1 slot available. I tried adding a VisionTek ATI Radeon 9250 PCI card after the Microsoft Windows 7 compatibility page indicated that this card was compatible. However, it didn't work because the card only supports DirectX 8, and Windows 7 requires a card that supports at least DirectX 9. I also tried a Matrox G450 Quad card in the PCI slot. However, it wouldn't allow me to use the 4670 at the same time. In addition, although I got all four monitors to display something, the resolutions for my two widescreen monitors weren't supported and as a result could not be properly displayed and I couldn't get any video players to work on these displays at all. Can anyone recommend a card that will work for me? The monitors attached to this card would primarily be used to display stock charts using Tradestation.
Have you looked at any of the new Radeon 5000/6000 series? Some of those cards have eyefinity versions that could replace your 4670, but are kind of expensive. Those cards use six Displayports but usually come with a few DVI and HDMI adapters so that you quickly set up a few monitors. Displayport adapters are expensive (you might need the active kind) but these cards enable to connect up to six displays at a time.
+1 mister g
Along with purchasing a newer 5xxx/6xxx series card, he may also have to replace his PSU, because usually OEMs ship their computers with pretty crappy PSUs, say if he decides to go for a 5770 or 6770 he may need a good quality 400-500W PSU.
I would suggest you to consider these implications, and tell us what is your total budget for this upgrade.
The problem is though they don't make AGP cards any better than the 4650. To upgrade the OP would have to do it through PCI and the Radeon 5450 is not as capable as the 4650 in many other HTPC functions.