I have a 500 watt power supply in my pc, I would like to to replace the current video and soud cards. Will a 350 watt or greater sound card and a 500 watt video card function properly on that 500 watt power supply?
It depends on what else you're running and the capacity of your 12-volt line. The specs for the video card say it wants 26 amps. Use a PSU calculator like the one at Cooler Master
to determine how much PSU you need, and then beef it up 20% for luck. Look at the label on your now or future PSU, or look it up online, and be sure it has enough 12-volt amps on the line you'll be powering the video card with. That card, the 9800 GT, comes with an adapter so you can power it from a hard-drive power plug. The sound card will not pull anything like 350 watts, more like 35.