Some help with PSU choosing and general system mark req

Hello, I intend to buy new PC in few weeks. Nothing fancy, but not total crap too. But the biggest problem I've encountered is choice of PSU wattage. And I'd like if you'd check my build and give your opinion.

CPU: Intel E8400 Core 2 Duo LGA775 3.00/1333FSB/6MB... blabla, ton of things
Mainboard: MSI P7N Platinum
HDD: WD Caviar SE 16mb 500gb
VGA: Sparkle GeFORCE 9600GT PCI-E, 512MB DDR3
Case: MODECOM CASE BLACK,LCD,USB,TAC,FAN80
PSU: CHIEFTEC PSU ATX/EPS 550W PFC 12CM 27DB
DVD: SMG DVD+/-RW DL RAM 20X BLACK SATA

Yes, I'm buying single 9600gt for now, but in a few months second is coming, so with this said arises question. Will my 550W PSU be enough(I checked it for double vga connectors so it's np). Main question is wattage.

Thanks in advance, sorry for poor english.

Get a WD 640GB, it's way faster than the 500GB.

550W is enough even if you add a second 9600GT later. I'd pick a Corsair 650TX for example or a StealthXStream 600W or GameXStream 600W instead, if possible, just because they are more reliable brands.

How much does MSI P7N + two 9600GT cards cost where you live? How much would a P5Q Pro + two HD 4850 cards cost? If the difference is not too big you should get the P5Q/4850 combination, it's a better chipset and the cards are faster.

In my country P7N+two GF9600GT cost about 260 pounds. Single HD4850 costs about 110 pounds with some % off. I'm little tight on budget -_- I already squeezed this configuration to minimum due to money needs on other things. Besides P7N is being praised my many websites, that's why this choice.
And in my country not every single psu is available. I have Zalman available, but those cost load of money. Thanks for help, much appreciated