What do i need for Intel q9550 and...

if the price not a matter then
ASUS Maximus II Formula LGA 775 Intel P45
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
or
any p45 boards
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
PSU
cosair 620w
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

cooler i cant recommend better than XIGMATEK HDT-S1283
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Look at the cooler reviews here at www.frostytech.com They rate them both for cooling and for quiet. If you're using a single HD4870 then go with a P45 motherboard. Asus or Gigabyte.
Look for RAM that is DDr2 800 1.8v it will be fine for you and less hassle for a beginner
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
or
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
any good quality 550w or above power supply, Corsair, PC Power and Cooling, Antec , Seasonic or OCZ.
Good recommendations by chechnyan

Is there any problem with the memory i choose?

Not really, it's just that it's DDR2 1066 and requires 2.1v to reach it's timings. It will be a slight bit faster once set in BIOS , but may cause a bit more hassle. Unless you're going for a serious overclock, the DDR2 800 would be fine for you.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
your call

1. I would change the RAM, Dominator is expensive and its 1066mhz which has no real benefit unless your a super clocking or want to run any other ratio than 1:1. As suggested by dirtmountain 800mhz will be great and cheaper.

2. P45 is a good choice still gives you crossfire if you need it as well   Asus P5Q is a good range (P5Q-e is best feature/$$ board)

3. Corsair 620W is a nice choice agreed.

4. If you want silent you want a 120mm fan, and as suggested the XIGMATEK HDT-S1283 is one of the best out there and cheap   others would be Thermalright Ultra 120 and Tuniq towers (you need a big case though.)

Thank you all for your help.

i am building a gaming computer this chirstmas. is this good? can it play CRYSIS on VERY HIGH?



EVGA GeForce GTX 280 Video Card - Superclocked Edition, 1GB GDDR3, PCI Express 2.0, FREE Special Edition EVGA Precision Overclocking Utility, SLI Ready, (Dual Link) Dual DVI, HDTV

Intel Core 2 Quad Q9550 Quad-Core Socket LGA775, 2.83 GHz, 1333 MHz FSB, 12MB L2 Cache, 45nm (Retail Box) (BX80569Q9550

Asus Striker II NSE Motherboard - nForce 790i SLI, Socket 775, PCI-Express 2.0, 3-way SLI, 45nm Support, USB, eSATA, RAID, Firewire, DDR3 Memory Support


Ultra X3 ULT40064 1000-Watt Power Supply - ATX, SATA-Ready, PCI-E Ready, Energy Efficient, Modular

Seagate Barracuda 7200.11 1TB Hard Drive - 7200RPM, 32MB, SATA-300, OEM


Corsair Dual Channel 4096MB PC12800 DDR3 1600MHz Memory (2 x 2048MB)

That RAM wont work with that board for a start.

And i dont understand why going for a Quad if your only GAMING. An e8400ish would suit you better. OC better and no need of quads for gaming. Read a bit of benchmarks you'll see.

Hi.

I got Intel core 2 quad Q9550 @ 2.83GHz
(nVidia) FXF GTX 260 896mb VGA card
4Gb of RAM
1 cd drive
Asus P5Q motherboard
and Antec sonata III with the 500w PSU

I gonna buy Noctua NH-U12P cpu cooler
and will try to overclock my cpu to 3.5 - 4GHz

Do i need a new power supply???

Right now my vols are something like
3.3V = 3.29
5V = 4.97
12V = 12.01
Something like that