http://en.wikipedia.org/wiki/Nehalem_(microarchitecture)
For more info on Nehalem, including prices.
As for the tri-sli 280gtx, I think you will need more than 850watt power supply though, not sure though. I think a 1.2k power supply is what is recomended going off memory, but if your waiting till next march than by than the 280gtx will probably drop in price and no longer be top dog.
And Nehalem will most likely be worth it, espically since the price difference probably won't be too outragous when it comes out (after a few months most likely), since they are trying to get people to build all new machines (ddr3, and new socket so they new a new mobo) instead of price gouging it out forever.
Oh and just a little note on intel's extreme cpu's is that it is just an ordinary CPU with the multiplier unlocked so it is easier to OC, but you can usually push the normal CPU's high enough as it is. So it's probably worth looking into OC a normal CPU than buying the extreme, you can save quite a bit of money that way. I recomend reading the article that is stickied on how to OC an duel/quad core CPU before thinking about buying an extreme edition CPU, as I be surprised if you couldn't push the standard version to how fast the extreme edition comes "stock".
And if you ever do go the water cooling route, research it thoroughly, and you can usually find some really knowledgeable people on the forums concerning that (im definately not one of them). I definately recomend posting on the forum or talking to someone knowledgable in this area before buying anything to do with watercooling since buying an inferior part can be costly if something bad happens, or it just may be rip off and provide inferrior cooling. I also heard something about being able to use a non-conductive liquid instead of water which may be worth looking into, as it may save you big time incase something bad happens and you spring a leak. Though personally I doubt you need a water cooling system as long as you get a good CPU heatsink and case. Which that cooler master case will definately provide good ventilation and look good doing it.
Oh and just something else I thought of when you mentioned your age. If you do end up building a very hi-end power hungry machine make sure it's alright with your parents, as it may just raise the electricity bill a bit if you have it on all the time. And just for reference just because a power supply says its a 850watt power supply doesn't mean it will draw 850watts, it will only draw as much power as it needs, so naturally it will use a little bit of power when idle and alot when it's under a full load.