New Build Component Check

Hello everyone. I'm looking for a little assistance with component selection for a new build. You've been great to my friends who have come here in the past. So I have a lot of respect for this board.

What I have:
Old systems parts, Case, Power Supply (500w), I/O, Hard Drive (Sata)

What I need:
MB (onboard sound and LAN), Proc, Video, RAM, maybe Power Supply?

What I'm planning:
I'd like to use this as a gaming rig / video station. I'm aiming to comfortably be able to play Left4Dead, Fallout 3 and any of my old favorites. I also do a lot of video conversion so I'm thinking quad core. Also, I'm not really interested in over clocking this system or SLI / Crossfire. Although, I'm not going to turn down a motherboard that offers me some options in the future.

I have some rewards points through my credit card that I've redeemed for gift cards at an electronics retailer. They price gouge but I've selected a proc and some video cards that I think I'll be able to live with. They're effectively free…so I'll definitely live with them.

What I'm looking at:
Intel Core2Quad Q6600 (2.4, w/1066FSB, 8MB L2)

EVGA GeForce 9800 GT 512MB (PCI-E 2.0) or
Diamond Multimedia Radeon HD 4850 GDDR3 512MB (Not PCI-E 2.0?)

What I'm hoping for assistance with:
I still need to select a motherboard / RAM combination. I'm hoping to spend no more than $200 up front…I figure I can settle with 2GB of RAM right out the door and add more next month when I can budget it in. I'm also hoping to be able to use my existing power supply. But I'm not sure it will be up to the new requirements. I'm also conflicted on what video card I should go with. Traditionally I've fallen on the Nvidia side.

So that puts me in the $150 range for a motherboard.
And about $50 for RAM initially.
And if needed I'll find $100 to $150 for a new Power Supply (120mm fan preferred)
I currently have a Seasonic 500HT.

What do you think? Any advice would be great…I'm really hoping to avoid any hardware *gotchas* on this build.

Thanks in advance.
Kevin

The Diamond HD 4850 card is in fact PCI-E 2.0. Here's a link to the specs on Newegg:

http://www.newegg.com/Product/Prod [...] 0&Tpk=4850

The 4850 is definitely the faster card. The 9800GT is essentially a rebadged 8800GT.

I would also highly recommend this motherboard and RAM:

GIGABYTE GA-EP45-DS3R LGA 775 Intel P45 ATX Intel Motherboard - Retail
http://www.newegg.com/Product/Prod [...] 6813128344 $126.99 -$20.00 MIR

mushkin 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory - Retail
http://www.newegg.com/Product/Prod [...] 6820146731 $76.99 -$20.00 MIR

What OS are you running? You'll probably want to upgrade to 64-bit to fully utilize all 4GB of RAM.

Microsoft Windows Vista Home Premium SP1 64-bit English for System Builders 1pk DSP OEI DVD - OEM
http://www.newegg.com/Product/Prod [...] 6832116488 $99.99

Your current PSU would probably be OK. If you do end up upgrading it, buy.com has an amazing deal on the Corsair 750TX.

CORSAIR CMPSU-750TX TX 750W Power Supply Retail
http://www.buy.com/prod/corsair-tx [...] 78325.html $103.74 -$20.00 MIR

$84 shipped after MIR!

Edit: dirtmountain beat me to it.

No, DDR2 1200 is not worth the money. The Mushkin RAM is desirable because of it's low timings (5-4-4-12) at the standard 1.8v. It's also pretty cheap. Any DDR2 800 RAM at over 1.8v is already factory overclocked/overvolted which will probably not leave as much headroom for your own overclock. The RAM should also run cooler and last longer since it isn't overvolted.