It's more than likely going to be fine. Just as a point of reference my machine is:
8GB (2x4) DDR3-2133
2x1TB 7200RPM drives
When I plug my machine in to a kill-a-watt, in general usage my power from the wall is about 120 watts, while playing games it's about 160 watts, and if I run a CPU, GPU, and 3xHDD benchmark to peg everything all at 100% it's 220watts. Keep in mind that this is from the wall, and since my power supply is about 80% efficient or so that means in each case the power supply is actually supplying 96, 128, and 176 watts respectively.
If you take a look at http://www.anandtech.com/bench/Product/647?vs=549&i=413.412.414.415
you will notice your video card doesn't use all that much more power than mine does. I'm sure you are well under your 500w as long as it's not some weird 'super dee duper ultra mega brand' supply.