You might get by, by purchasing a card without a 6 pin PCI-e power connector. A couple of years ago the HD 5670 should have worked. There may be newer, better models.
I'd pay attention to the power recommendations by the manufacturers for these cards but a little cheating if your power supply is decent can be done.
Here's a half decent Power Supply at a good price that will upgrade your video card choices.
http://ncix.com/products/index.php?s...c&promoid=1015