The choice of MB really doesn't matter much as long it has most
of the features you need if you're not OC-ing. But if I have to
pick, I would go with Gigabyte's GA-P35-DS3 going around at $205
(not our dear giga 
).
Erm, for that 3x 8800 Ultra, I'm not serious about it. 
Seriously, each 8800 Ultra costs more than $1,000. And the entire
setup will easily cost more than $6,000. It's like a Mercedes-Benz
- too fast, too expensive. You can read more about its review
here.
http://www.guru3d.com/article/Videocards/481/
A 8800 GT (512 MB) or 8800 GTS (512 MB, not the 320 MB or 640 MB
one) which cost around $450 and $550 respectively would be much
more worth the $.
Processor-wise, get the Q6600 which is retailing at $440. Iirc, the
next CPU in the Quad series is double that price.
For RAM modules, stay with DDR2 ones. The DDR3 sticks do not offer
much performance advantage against DDR2 ones, but each one costs
around 5 - 10 times more than its DDR2 counterparts atm. For a good
balance between cost and performance, grab those DDR2-1066
low-latency modules like HyperX or BallistiX which is going for $80
- $110 each for the 1GB model. Otherwise, go with the DDR2-800
Value RAMs selling for around $40 per 1 GB stick.
To get the most value out of hard disk drives, go for the ones that
are between 250 - 500 GB as they have the lowest $/GB ratio (approx
$0.40/GB). I would pick one from Hitachi, and Anty would recommend
you Seagate. Anyway, if you are looking for performance, go with
Western Digital's Raptors ($2.30 - $4.20 / GB depending on model).
They get pretty hot easily, so you may need good ventilation for
your casing.
I'm not experienced with cooling systems, but I suppose you will
need cooling for CPU, graphics card and casing individually or even
water cooling only when you're OC-ing. These components should not
sweat under normal use. Anyway, a good CPU fan typically cost
around $100. Or you can just use the stock fan that comes with the
CPU. Not too sure about the rest.
Other than all these components above, do remember to factor in the
cost of the power supply unit (good ones go for $150 and above,
infamous ones go for $50), the casing (walk around SLS to see-see,
nice-looking ones cost between $80 - $180), the monitor ($250 -
$450) and if the MB doesn't have a good on-board sound card, you
may consider getting one. The cheapest would be around $50
(Creative Audigy) which can be said to be above most on-board sound
cards.
And some general advice here. No need to use until up Lorry` de.
You can consider upgrading every year and selling the parts off at
30% - 50% of the original price at forum marketplaces which can be
used to supplement the cost of the upgrade itself. I personally
find this way to be more worthwhile. It's like having a high
startup cost on the first purchase but enjoying high-end tech stuff
at 50% - 70% of the original price on every upgrade.
