prodromus

I've owned cards from both companies and neither is de facto better. When you are ready to buy your card, you should go for the best "bang for your buck" card available at the price point that fits your budget.  For a quick and dirty overview I recommend checking out Tom's Hardware for pretty good break downs of the best video cards at each price level (newest edition just came out here).

Yeah, I had a ton of fun playing with some friends last night.  We had some server problems getting a game going at first but later on we restarted steam and it downloaded a small patch that seemed to fix things.  On the higher difficulty levels it's really fun and I can't wait to play as the infected.

PC specs: AMD X2 6000+ (3 ghz), ATI 4850, 2gb ram- runs perfectly 
My friend has: AMD X2 3800+ (2 ghz), 7900 GS, 2 gb ram and he was running it fine as well.

One reason to get a quad would be if you run other things in the background while playing, voice chat software, a web browser with an FAQ, etc. Because separate programs will run on their own core so even if the game only uses 2, other programs can use the others and will steal less performance from the cores running the game. That being said though, right now benchmarks show a fast dual core outperforming a lower clocked quad core in almost every game.  Unless you are doing audio/video encoding or autocad or something the quad loses almost always.

15 or so, I don't have as much time to play games as I used to but I love steam.  Pre-loading is awesome, I buy all of Valve's stuff on Steam.

If you have 512 mb, you definitely don't have DDR3 ram, but Foil's point about making sure you get the right ram for your system is a good one.  I would recommend 2 gig for now.  You can't actually use 4 GB unless you are running a 64-bit version of windows, your system will only see about 3.5 GB or less of it. 

If you have one 512 MB chip, you can buy a second one and add it to get 1 GB.  If you have 2 x 256 MB chips, you'll need to replace them unless you have 4 RAM slots.  RAM is cheap, depending on the brand you can get 2 GB for $30 or less. And given the weakness of the dollar right now that's probably about 2 pounds. :) 

Yeah, the 4850 is a better deal right now- not much more expensive and considerably more powerful.

For future reference, the reason there are so many different 8800GT cards is that Nvidia makes the graphics chip on the card and releases references specs for the card.  (So any card you buy will at minimum be as good as Nvidia's reference specs in theory) However, Nvidia doesn't actually manufacture the cards, other companies (like EVGA, XFX, ASUS, etc) buy their chips and make the actual cards.  Sometimes these companies make changes over the reference specs such as overclocking them, or adding a bigger heatsink/fan.  This same process holds true for ATI cards as well.  Not all brands are the same price or the same quality.

Yeah, but P4 is pretty old tech.  A decent dual core will give considerable performance benefits both in-game and out.  Also, wattage isn't the only thing that matters on the power supply- as has been mentioned you'll need to make sure you have enough amps on the 12+ volt rails.  How much depends on what proc. you end up getting but this can affect stability just as much as wattage.

If you get a system that plays current games at max settings, it will be 3-4 years at least before you are playing on lowest settings.  You will gradually have to lower the settings you play on as newer games come out with more demanding specs, but it will be quite a while before you are playing on low.  My system wasn't running stuff on highest settings when I built it and 2 years later it runs new games quite well- nowhere near lowest settings.  If I had started with a high end rig I'd be doing even better.

Yeah, it was a great show.  The basic training stuff they put out was a good primer for beginning players. Just be aware that due to balance changes in various patches that have come out since- not all of their information is still up to date.  There is a show on the gamereplays.org CoH portal called Drophacked that has both audio and video episodes if you are interested in current content.

Neotheta- if you're considering the 9800 GTX you should keep your eye on the 4850- it compares very well performance-wise to the 9800 gtx and is a bit cheaper.  But with the price wars currently underway, the prices on both are likely to change in the next couple of months.  One thing is for sure- competition is good for the consumer.