If your power supply is the 250W model, you are very limited. Limited to a card that only requires the 75 watts that your PCIe x16 slot provides. The HD 5570 would be the max size card I would try. If it proves to be too much for the PSU (I doubt it), you will know. The system will shut down or reboot. Here is one for example: http://www.amazon.com/Sapphire-Radeon-HD-5570-PCI-Express/dp/B0036ORMYO