you don't need a 9800 at this moment, there are no games out at the moment that need that much gfx performance and DX9 like HL2 or doom3. I wait till september. In some cases it could save me 100 dollar.
If you run a game with no AA and AF, then run it with say 6x/16x it looks 100x better, the thing is though that your FPS get cut in half usually once you run the above numbers for AA and AF. This is why new cards are released all the time. If you dont run AA and AF then a card such as a ti4600 or 9500pro will run games at good FPS for another year or so.
Also gaming at high resolutions effect your fps..another reason for faster cards