1) Sound card was only around 2-3k. A cheap 17" TFT is of no use and will become a hurdle when you need to reduce the res in newer games. Get the 17" CRT period.
2)I don't advise 19" CRT, it should be around 10k, a good one might be a little more. On a 19" CRT you won't like to play below 1280X1024 because of the very low pixel to area count, lines and all you know. But the system you are getting will need to play many games at 1024X768 that too which are already released and the future is all 1024X768 for a 7900GT. So a 19" monitor will probably make your games look like crap unless you lower the graphic detail which also is not what I would want. Therefore a 17" CRT is your best bet.
3)7600GT SLi>7900GT, but then you need to get a better power supply, spend a bit more, get a slightly more expensive motherboard, rather spend 5-7k more and get the 1900XT! And a 7600GS SLi is not advisable, though you should research your bit. 7600GT SLi will surely be better. But you are forgetting that if you get the 7900GT with a good cooling solution and volt mod it and overlcock it, it is one hell of a card and competes the 7900GTX!
A notebook is not meant for gaming as a PC is.
I know that I am exceeding your budget, but at the end it will be worth it. If you want to save some dough, consider X2 3800 (939) + Asus A8N E, which is surely less future proof but stilla good gaming solution especially once overclocked or even AMD 64 3500 + Asus A8N E and overclock it past 2.6GHz speeds with good cooling solutions.