Sterling, which is the order entry system used by most guys, doesn't take a lot of power. I'm running it on a P2 400mhz with two dozen time and sales and two dozen level two screens open and it runs without a glitch.
Instaquote, for charts, seems to run fine on the same computer, but I'm using it mainly on a P3 650mhz machine. I only have a couple charts open at a time though. I use qcharts for my main charting.