Firstly, I would recommend getting a 32 bit OS rather than a 64 bit one as there are a lot of compatibility issues with drivers etc. at the moment.
If I was buying a gaming system today I would go for an ATI 4870 graphics card (click here). The Nvidia 8800GT in your system has been around a while now and starting to become dated, even if it is an SLI setup.
If you do go for 32 bit Windows then it will only be able to see a maximum system memory of 4GB (that includes the RAM on your graphics cards) so you may as well just buy 3GB for the motherboard.
Apart from that, everything looks great.