I have had trouble with nVidia drivers in the past on an old GeForce2GTS/Pro card. It reported the number of texture layers wrong and this caused me considerable problems so I had to stay with an old driver for about a year until eventually they fixed it (or did I upgrade my card?).
I do not experience much slowdown with my current nVidia card (5200FX) and 2D commands, infact I invariably have quite a few text commands onscreen - it's a near instant command.
My immediate thought on reading your problem was that your Blitz was not up-to-date.
I have not looked at your source code but looking at the demo I see no obvious reason why something like that should not run a lot faster, I only got 32fps here. 2Ghz AMD, 512mb Ram
I do not experience much slowdown with my current nVidia card (5200FX) and 2D commands, infact I invariably have quite a few text commands onscreen - it's a near instant command.
My immediate thought on reading your problem was that your Blitz was not up-to-date.
I have not looked at your source code but looking at the demo I see no obvious reason why something like that should not run a lot faster, I only got 32fps here. 2Ghz AMD, 512mb Ram