The answer to your question is an unfortunate No.
Running two graphics cards is done by using a mode called SLI (for NVidia cards) or Crossfire (for AMD) cards. I'm pretty sure the GTX 285 doesn't support SLI mode. But even if it did, SLI/Crossfire mode require the two graphics cards to be the exact same card.
Running both of your cards on the same PC is not possible.
That being said, the rest of your PC is a very good build. While a little more RAM would be preferable, you can play games without any graphics card on low-ish settings. I do not know how powerful your PSU is, but if it is at least 500W you could get a nice new 750TI for $150 bucks and enjoy medium to high settings in new games.
Also, you asked about the pros and cons of SLI/Crossfire set ups. Even though you do not have the ability to do such a thing with your cards, I will still tell you a little bit about using two cards. As I mentioned earlier, the cards must be the exact SAME MODEL and be running at the same clock speeds. SLI works by attaching an SLI bridge to the cards, which allows them to work cohesively. Essentially, each card will be doing half the work. One renders a frame and stores it in VRAM for a moment while the other card renders the next frame. By using two cards, you typically see increased FPS in games. Keep in mind, just because each card has 2gb, for example, of VRAM does not mean that you have 4Gb of VRAM. The cards essentially duplicate everything before they send it off the CPU, so you don't get any extra VRAM from an SLI setup. Some more cons include, micro-stutter, increased temperature, and increased noise. Micro-stutter is when the frams rendered by the cards are not put together so smoothly because they are coming from two different cards. A good CPU (such as yours) usually does not have a big problem with this. Second con: a GPU generates a lot of heat. SLI/Crossfire requires the cards to be right on top of eachother, sandwiching a lot of that heat between the cards. This can be very bad. A good and often expensive cooling solution is therefore needed for SLI/Crossfire. Third con: More graphics cards means more fans and faster fan speeds. This simply makes everything louder. That's more up to personal preference though, because many gamers wear headphones, and some even like noise because it tells them that their baby is being kept cool.
Anyway, I hope my rambling about using two cards has given you something to consider. But at least you now know that you can't use both of your cards at the same time. Hope I helped!
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