Let me mention 2 cards I own and have put on a Watt Meter (similar to the P3 Watt Meter).
Both installed in machines exactly like yours so comparisons are doable and maybe interesting to you.
1. A Nvidia 9500GT with 512MB. The socket 939 box tops out at 120 Watts in total and idles at 70ish Watts.
I tried an ATI card but it pegged the CPU so I went with Nvidia.
2. A Nvidia GeForce GT 220 1024 MB DDR3 PCI-Express Graphics Card http://www.amazon.com/gp/product/B002SG7LUQ/ref=oss_product
I chose this because of the Watts but also because the next model up had complaints of fan noise.
The GT 220 on a HP d4999t w/4GB RAM, etc tops out at 140 Watts and is very nice.
I'd consider item 2.
Well, I did search some. And I hesitate because someone will say not upgrade this old rig. Abit AN8 (ultra), socket 939, Athlon 3500+ @ 2.47 Ghz, DDR400 ram, 4 Gig Matching Corsair XMS, nForce4 chipset,
I'm running W7 64 and it runs Areo.
I was thinking to upgrade my 6600le NVidia. I was sorta looking at Radeon HD 4850, or maybe a 56xx or 57xx series.
1. Can I over kill on vid card so much as to cause problems??
2. Since everything about this mobo is Nvidia, will this old hardware "like" a new Radeon card as well as it might "like" a new NVidea?
You wonder why spend money on old set ... I dunno, I LIKE my old box, I guess I just want to see how far I can max it out. My retirement income is such that I can find extra $100 once in a while, but if I build new, I would not be content to go low end. And long as this box runs well, I can't justify spending that much.
Anyway, please Advise, Criticize, or Insult. I want to hear it.