Planning to buy a GTX280. What should I think of/have in mind before purchase?

Hello guys.

Today I have a single XFX 8800 GTX, which is working well. But considering the bigger need of high-end hardware these days, I will yet again upgrade.

Now.. Since I quite lack the skills needed to know which kind of parts make a good computer I turn to you.

Should I stick with the XFX-manufacturer or change? I know XFX is good but is it outmatched against another manufacturer, such as evGA?

And, the most important thing, what additional things should I have in mind when buying? What about the Power supply?

Today I have a Silver Power PSU, 600W, with a 120 mm fan, Blue light, ATX/EPS, 2xpci-e, 20/24 pin.
Since this came with the computer and I hadn't heard of it before I suppose it ain't good, but have in mind that I just need parts suffice to handle the card itself with no drawbacks/Bottle-necking.

I have a C2D E6850, which in my opinion is okay for this year out. It's not a vast processor, but it's no sucker either. Still, I know processors are getting cheaper, but I will stick with it if it's enough for the card.

Have 2 GB of RAM which, of course, will be doubled soon since Vista, along with games as Crysis, eats it away.

Now, what do you guys think? What must I KNOW before/after buying?

TIA /// HEavy.

Vista doesn't "eat memory." It utilizes it. It's not "lost" when consumed, its put to work in a way XP can't. (But yes, 4gb is better ;)) The only drawbacks to the GTX cards are as follows: Size, lack of DX10.1, lack of HDMI audio. The 2nd drawback is a non-factor right now, but that could change. TBH I'd go for EVGA just to give yourself some piece of mind in knowing that if a better card comes out within 90 days, you can upgrade to it and pay the difference. XFX is fine if you intend to keep it for its lifetime. That said, the 55nm revision of the GTX 280 is right around the corner, so you should probably wait for that to drop if you want to be top dog for a bit.

I don't mention BFG's trade in program because if I'm to understand their website right, they don't refund the purchase price of the card you trade in, only its "market value," which I assume will be lower than what you paid.