| The first system sounds a bit better - newer and faster CPU, better power supply, more storage (also has matched hard drives so you can RAID them if desired). It's missing a sound card, but unless you're an audiophile you'll probably be satisfied with the onboard sound.
Graphics card choice is probably the most important factor for gaming, and should be determined by your monitor's resolution. If it's 1920x1200 or less, a single Radeon HD 4870 or 4890 with 1GB graphics memory should be sufficient; dual GPUs are usually overkill unless you're running at higher resolutions, and you can always add a second card later if you feel the need to upgrade. ATI cards are generally a better value than Nvidia cards right now, and I've never had any issues with their driver support. In fact, ATI releases new certified drivers every month with new features, optimizations, and bug fixes, while Nvidia doesn't follow any regular schedule (which can be frustrating if you happen to run into a problem).
I'd also recommend adding more RAM to this system... it's cheap and you'll be running a 64-bit operating system, so there's no reason to limit yourself to 3GB. Go for 6GB at least. | 
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