> >3. You might also consider upgrading your GPU. I bought a >GeForce 9800GT for just over a hundred bucks. These cards are >SLI and so if you later find that your system seems to be >"bottle-necking" again, you can >"daisy-chain" two of these cards together for 2X >video performance! Furthermore, this would allow you to us a >dual-monitor setup and, as NX2 does support this feature (very >nicely), you could display your workspace palette's and other >support applications on one monitor and display your graphics >(i.e. NX2, CS3) on the other. I just bought a 22" LCD for >$130 bucks (that's pretty cheap for the this added >flexibility)!
I agree with adding 2 more GB or RAM to improve performance. But a GeForce 9800GT would, at best, be equivalent to your 6600. If the 9800 had more graphics memory than your 6600 then it would be a downgrade. Two GeForce 9800GTs would be a considerable downgrade and would obviate any benefit that 4th GB of RAM might provide.
You do not want to use any more graphics memory than you absolutely need when building a photo workstation. There is nothing on a GeForce 9800GT that would provide an advantage over your GeForce 6600 for photo work. Photo work does not require 3D graphics processing or fast refresh, and it needs very little graphics memory.