I had a Dimension E510 which was the rough equivalent of your Dimension 9200. The first question is what kind of functionality are you trying to get out of your system? Do you want to play games, or is it more of a basic use machine for the internet, word processing, spreadsheets, video, music, etc...?
The limiting factor in those machines is the power supply which lacks any PCIe 6-pin power connectors which limits you to video cards which use the motherboard's power supply without spending an additional $100+ on a new power supply. In this case I would recomend you check into a Radeon HD 6670 with GDDR5 memory which will run around $100 and will provide the best 3D performance possible on your current machine. If you're looking for something a bit more basic than that because you're not into games or you're on a budget then I would suggest the DDR3 version of the same card which will run around $70. Both of these cards will provide performance which is magnitudes better than the now anchient nVidia 7000 series cards while using less power and probably costing about the same as the difficult to find older cards.