I just bought a second monitor, I have two Acer P191 screens.. What kind of graphics card do I need to support them? My comp is Acer - Desktop with Intel® Pentium® Trip.l-Core Processor E2220
I don't know what type of motherboard you have, but most likely you've either got a few PCI or PCIe slots available. The cheapest thing to do is just go pick up 2 identical video cards and pop them in. If you think you might ever want to attach more monitors than what you have available slots for, then you can get a dual monitor video card which will only take up one available slot. As long as you buy all identical cards, you shouldn't have too many problems.
Most graphics cards will work. Just make sure they support "DUAL" monitors (SVGA or DVT output). The important question is to know what bus your Acer computer has, and find the card (they have different bus types) to match. I use a few PNY cards myself.