I always love how folks answer questions like this without even asking the OP's resolution. LOL
Regardless, the GTX 280 should play Metro 2033 fine as long as you're using DX9 mode like you suggested. Though the game is really meant to be viewed in DX10/11. Can be fairly amazing image quality that way.
You could possibly play it in DX10, with lowered settings depending on your resolution.
It's a beast of a game. With DX11 @ 1920x1080 my GTX470 averages about 30FPS.