Building a gaming computer

Hello, I'm going to be building a new computer, along with asking a lot of questions. I'm thinking of spending roughly $300. I will be using the computer for gaming.

I already have the following leftover from my old computer:
Monitor - Crappy old CRT, it works.
Case - It's huge! http://www.newegg.com/Product/Prod [...] 6811124121
PSU - Tiger Model: ATX-450W-P4
+5v -5v +12v -12v +3.3v +5vsb
35.0A 0.5A 16.0A 0.8A 24.0A 3.0A
CD/DVD - One DVD and one CD drive.
Hard Drive - 160GB + 40GB


I'm trying to figure out what my best bet to upgrade is. Roughly $300. I'll need a new motherboard, processor, RAM, and video card. Just a rough sketch of my thoughts:
Motherboard - I have no idea.
Processor - Athlon X2 3.0GHz: http://www.newegg.com/Product/Prod [...] 6819103233
Video card - 9800GT: http://www.newegg.com/Product/Prod [...] 6814150316
RAM - 2GB: http://www.newegg.com/Product/Prod [...] 6820231098


Questions:
- Should I wait for the i7?
- Will I need a new power supply?
- What would be better price/performance? And Intel or AMD? Suggestions on a motherboard and processor combo?

Thanks for any help!

I cannot readily find information on that PSU. It does not have anywhere near the power for a 9800GT. As Proximon says, it is probably even worse than the numbers suggest.
A $300 budget doesn't go very far.
The following list will START you toward a build. I am assuming you also have an O/S, keyboard, mouse, and speakers.

GIGABYTE GA-MA790GP-DS4H AM2+/AM2 AMD 790GX HDMI ATX AMD Motherboard - Retail
Item #: N82E16813128352
-$10.00 Instant

$128.99

Antec Basiq BP500UB 500W ATX12V Version 2.01 Active PFC Power Supply - OEM
Item #: N82E16817371019

$39.99

A-DATA 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model ADQVE1A16K - Retail
Item #: N82E16820211066

$34.99

AMD Athlon 64 X2 5000+ Brisbane 2.6GHz Socket AM2 65W Dual-Core Processor Model ADO5000DOBOX - Retail
Item #: N82E16819103211

$59.99

Subtotal: $263.96

There is no video card there. The integrated HD3300 GPU will actually play some games. Guild Wars, for example, with good settings, will play at over 50 FPS on a 1440x900 monitor. When you can afford it, however, the PSU I have included can handle up to an HD4850.
Really, if you can get up to $500, you get into the realm of a much more satisfying Intel build.

That mobo is nice, except that he does need video, which then breaks the budget. In that case, the one I'd choose now is this 4670 for $70 after MIR: http://www.newegg.com/Product/Prod [...] 814121274. It's on the same performance tier as the 3850, but needs less power.
The memory needs 2.1V to achieve its claimed timings. I always get RAM that will work at its advertised timings on the JEDEC default 1.8V. Plenty of people are happy to tweak their systems to make the other RAM work, but there are a lot of threads where others have had issues that boiled down to non-standard RAM. If you want no-muss no-fuss RAM, sticking to the standard is the way to go.
Jonnyguru reviewed a 500W Rosewill and was surprised it passed all their tests well enough to be recommended, because the brand as a whole is considered crap (and that model isn't the one that was tested).
@OP, if you can stretch your budget to $350, the CPU/Mobo that Sable suggested, along with my PSU, GPU, and RAM choices, would get you a better system than the AMD. Stretch to $400, and you can include a more robust PSU as well.

there should be a price drop somewhere in the middle of October i think next week sometime but i dont know if it will affect the E5200. Thanks jtt283 for revising my build i wasn't to sure about the PSU or the gfx card.

So basically you should get this:

CPU: http://www.newegg.com/Product/Prod [...] 6819116072

MB: http://www.newegg.com/Product/Prod [...] 6813128345

Memory you could either get the a data or this : http://www.newegg.com/Product/Prod [...] 6820146118

PSU: http://www.newegg.com/Product/Prod [...] 6817341010

and GFX: http://www.newegg.com/Product/Prod [...] 6814121274

total: 330
to make it fit in you budget you could get this memory: http://www.newegg.com/Product/Prod [...] 6820227124 it is 1.8v and you could get the 500 watt power supply http://www.newegg.com/Product/Prod [...] 6817371019

total: 300

For that budget I'd go AMD.

5400 BE $77 overclocking it will give you decent performance.
http://www.newegg.com/Product/Prod [...] 6819103289

This board supports 140W Phenoms
ASUS M3A78-EM AM2+/AM2 AMD 780G $76.99
http://www.newegg.com/Product/Prod [...] 6813131324

Mushkin DDR2 800 RAM 2GB (2x1GB) $44.69
http://www.newegg.com/Product/Prod [...] 6820146673

ASUS EAH4670/DI/512M/A Radeon HD 4670 512MB $76.99 + 8.25 shipp
http://www.newegg.com/Product/Prod [...] 6814121274

Which will give you a total of $283.92. As long as your PSU can put out at least 70% of its rated power you should be fine with that setup. Of course the cheap PSU won't provide you with the same stable power that a quality one would so your overclocking efforts my be a little limited. Even so you should be able to overclock the 5400 quite a bit. While the motherboard supports the Phenom processor, and should have no trouble supporting the new Phenoms coming out in the coming months, you should definitely upgrade that PSU before putting in a better video card or CPU. If you plan to upgrade again in a few months then I would say spend a little more on the motherboard and get this

GIGABYTE GA-MA790X-DS4 $109.99 + 9.39 ship
http://www.newegg.com/Product/Prod [...] 6813128075

This board will allow you to run crossfire graphics and by the time you get around to buying a second 4670 you should be able to get one for cheap. You can also go for a 790GX based board since the SB750 will help you overclock better. The new AM3 CPUs are suppose to be able to run on AM2+ boards. That should mean that you will have a good upgrade path going with AMD. We'll have to wait to see when they come out to know if this proves true.

that's also a solid build however you should never overlook a PSU as it is very important since its what powers everything in your PC

unfortunately i don't think the i7 MB will have the same socket so it probably wont work with the e5200 however im not sure. also the motherboards will be very expensive when first released so its probably better to go with the amd if you plan on upgrading later to another amd.

A new PSU sounds good, I've had some problems with loose and too short cords on mine anyway.

I don't have any preference whatsoever as for AMD vs Intel. So it comes down to which will be more upgradable: An LGA775 or AM2+ socket. I know LGA775 currently has more powerful processors out, like Core 2 Quads. But the AM2+ socket will be compatible with AM3 processors. Which socket would be best in the long run? Is it a complete gamble? I'm so lost here, guys.

.....after doing some research
alright the new intel boards will use socket 1366 so you wont be able to upgrade to that but you will still be able to get like a quad core that will probally be just as good as AMD the AMD board you can use AM3 CPUs but you wont be able to use the AM2 cpus in AM3 motherboards. SO either way i guess if you want to wait for the Am3 come to come out and be affordable than get the AMD but if you want good performance now get the Intel.