UltraVolta425

Definitely. At least for another 2-3 years, which is more than enough time to enjoy his profession.

Beyond any doubt: Windows 7. In my opinion, you'd either have to be nuts, or insanely old-fashioned and conservative, to still hold on to XP. It's old, ugly, it's got sooooooo many bugs that Windows 7 has not (anymore), and above all: to many common PC-users, Windows 7 is just as fast as XP, if not faster. But of course, same rule applies here, the same as with Vista: don't use it on an old/slow PC. Which isn't the case with your parts, ofc.

So get Windows 7.

If they don't, just sue them.

Kingston is indeed rather cheap and of good quality, and as long as your memory has the same speed as your motherboard (FSB) it won't be any problem.

Nop. Just make sure you know something about putting these parts together. Because computers are very expensive things to 'toy around' with. In other words, do be careful though.

Yep. I for myself have the Antec Twelve Hundred Case, and an ASUS EN9600GT card, which is the biggest I've seen in my life, and it DOES fit in.
So yours shouldn't be any problem either, I suppose.

Yep, they will. As long as it does an intake fan facing upwards.

Top-down, as in placing the up-side on the bottom of the case? No way, as long as your PSU has an upwards-facing air intake fan, just put it normally, like any other normal PSU, on the bottom of your Antec 300. If you can see the air intake fan, you'll know you're on the right trail.

At the moment, I have even less horse-power than you (430W), and yet I'm making fun of the graphics in games such as Crysis and UT3, so really, don't worry yet about the PSU. IF you wanna worry, rather worry about the graphics card, cuz that will form a problem much sooner than the PSU, I believe.

Yes. You posted this message in the beginning of September. We're 3 months later now, and things have changed quite a bit.
This is the setup I'd recommend to you, since it's more future proof, and yet, as far as I know, cheaper.

So:

====================

Intel Core i7 920 // 275 €
MSI X58m // 166 €
Corsair TR3X6G1333C9 6GB // 140 €

====================

The rest you could keep, but this little upgrade will keep your PC future-proof for a long while, I think.

JimmyJump

I also have an Antec 1200 and it has enough space for an ATI HD5970, which measures 30cm/12inch long. That's the biggest card ever made...

And when you're on a tight budget, better go for the i7 based on a LGA 1156 P55 chip. The Intel i7-860 is the most obvious choice (when going with Intel, that is) as that CPU sports Hyper Threading (comes in at between 240 & 290 euro, depending on where you buy), but the real budget CPU is the i5 750. Has a speed of 2.66GHZ but doesn't support Hyper Threading. CPU costs between 170 & 210 euro, again depending on where you buy.