Oh boy, I'm going to go against the consensus here and suggest you not do anything except save your money for a new machine.

Get BS2, but just run it at whatever settings the machine can deal with, then look forward to it running at full tilt on a new box.

If you must do something, get 4 GB DDR2 RAM. Yes, the 32-bit OS will only deal with 3.5 GB, but that will help. RAM is so cheap these days its worth it. Unless you part out your current machine, the 4GB RAM will be good for whoever gets the hand me down system.

What I said. Money wasted if the rest of the PC isn't upgraded.

Again, thanks for all the input. I purchased a 560 and 4GB RAM and installed it today. I figured if it really made no impact I'd bump up the motherboard and CPU too. In this case it was not so much the cost as the additional time needed to install a new MB. Maybe I will take that on in a few months, along with an upgrade to Windows 7.

I have not done exhaustive testing but so far just the RAM and GPU seems to have helped Black Shark 2. I am getting good frame rates, near 30 when cruising, and down into the teens when stuff really starts to fly. This at medium settings with my internal cockpit monitors (Shkval and ABRIS) at 512. This is better than I was getting at low settings with the 8800GTS. Task manager never goes above the low 90% on a CPU core, about the same as it had before (as expected).

I can also run a second monitor with helios with little or no hit so far, something I could not do with the 8800. I have not tried exporting the shkval and ABRIS to the second monitor yet.

Oddly I seem to get almost double the frame rates at medium settings vs low settings even when just sitting on the FARP pad. Low settings for everything except scenery, which is set to high in both so there are some buildings to hide behind.