AFAIK, you can't just buy any video card - it must be supported by the motherboard (e.g. you can't buy a cheap off the shelf cpu and buy a top of the line card). pls correct me if i'm wrong.
Generally... any new CPU and new video card you buy today will be compatible. There are likely only a few exceptions. (In the past, there have been exceptions... which the makers might have resolved.) Normally anyone who is buying a cheap CPU isn't primarily interested in gaming and wouldn't benefit much from a "top of the line" video card. And even if such buyer is a gamer, the hardware has a 99% chance of being compatible anyway.
I agree with winston. Square monitors are easier to set up. Vid cards are the last place to spend a bundle. Get something cheap off ebay.
it doesn't matter..i would worry more about trading system(if you have any) than PC. i'm using old, cheap,home made dual core PC with 5 years old monitor for my daytrading(10-200 transactions each day). it's more than enough for me. i can put one more cheap 10-15$ nvidia nvs card and have 4 monitors on same PC, but what for? +1 on LED monitors..less heat,more efficient
Op, take a look through some of the threads here about multi monitor trading hardware. There are numerous threads on this topic. Tikitrader even built a setup with pictures every step of the way.
I've traded with a Mac using ThinkorSwim (now TDAmeritrade) for a few years. They upgrade the software for both Mac and Windows.