The standard P5B isn't the best overclocker. get a Gigabyte DS3, a Biostar 965PT, a P5N-E, or a P5B around that price. All of those are great boards and overclock very well. The Card model "7900GS" is a good card but I've never heard of that brand and the 512MB version isn't going to help you at all compared to a 256 version. Get an XFX 7900GS or even a Foxcon over that one. I just have a hard time believing that brand will overclock much.
The RAM I'm not sure but it does say ATI so get this instead, I'm sure it will be just as good.
Get the Widescreen, I have that exact same monitor and no it doesn't just stretch everything out and become distorted. It looks very good and all new games these days support WS.
That Case is Very good for cooling and it's a good choice, as for the TV tuner I'm not to sure about.
Also I would get an E4300 and an aftermarket CPU cooler instead of the E6400 as you will need an aftermarket cooler and the E4300 has been to known to hit 4.0ghz sometimes.