Need help choosing the hardware for a 900 dollar computer

I'm looking for expert help, I need to choose the hardware for a 900 dollar computer, but I don't know what's best.
I need a 1GB graphics card, with DDR3 memory, PCI-E, 256bit. From what I understand, the best choice would be GeForce 9800GT or Radeon HD 4850 but I'm not sure at all. Plus, which manufactor should I choose for the graphics card?
For the CPU, I wanted to buy Intel Core 2 Duo E8400, because it seems it's the most popular, but I read many negative comments about it, and many people agreed that E8200 would be better (but it's 2,66 Ghz instead of 3...)
As for the motherboard, I have completely no idea what to choose, and I think it will depend of the cpu and gpu.
The same goes for system RAM, hard drive (250GB is enough, but I don't know what to buy), and pretty much everything else...
Kindly help me if you have the patience

EDIT:
For the sound card I picked Creative Sound Blaster X-Fi Xtreme Gamer. Is this ok?

The HD4850 graphic card, best value for performance right now. I like Visontek for graphic card, but as long as they have a decent warranty any will do.
E8400 or the E8500, check prices, there may only be a small price for the step up.
P45 motherboard- Asus, Gigabyte, Foxconn or Biostar, if you may want crossfire in the future, then get one capable of it.
Get 2x2 GB of DDR2 800 1.8v RAM.
Seasonic 7200.11 Hard drive if you go 250GB
The motherboard may have good enough sound for you, just use integrated sound, if it's not good enough you can add the sound card later.

Don't bother getting the X-Fi unless you have a really really good speaker setup. The HD onboard audio is suprisingly good on the new motherboards and it offers pretty solid sound quality compared to my Audigy 4 (I know it's not X-FI, but my point is the sound quality is pretty good already, save your $$).

Okay. I have a Z5500 setup with my system.

I use the Audigy 4 I have from my old computer and to be honest it feels no different than my onboard HD audio. I use two audio cards so I can vent (with a headset) and listen to music at the same time. Some people say Xi-Fi is a lot better than Audigy 4, I've only listened to it on my friend's computer, but I would have to disagree with that statement.

If you plan to do music compressions/recording, than I would consider getting a separate audio card for that.

Yes, the E8400 does contain a stock heatsink/fan and it works. I'm listing the Sunbeam Core Contact Freezer because it's a great cooler (not a waste of money). You can get a lot out of overclocking E8400 (a noticeable difference).

Because Mushkin rams have great timings at standard 1.8v (meaning it's great for overclocking and it's cheap). If you're not going to overclock, it's still better because it runs at lower voltages (less power consumption, less heat).

Then I'd suggest you look into the Asus Xonar or the HT Omega as well.

http://secure.newegg.com/WishList/ [...] r=10869108

Within budget, OC that e7200 to 3.5ghz without hassle, I'm sure it'll be great.

I wouldn't go with a Sonata because, in all honestly, it is very poorly ventilated. Though it's a nice bundle with that power supply, I'd opt for more headroom and expandability with a different psu, like the corsair one I mentioned. I picked that 4850 because it runs at very high clocks, its going to need good airflow, same for the processor. By having such high overclocked parts in the system, internal temps are going to rise- which makes the Sonata a bad choice for the case. I guess my last gripe about that case is how ugly it is.

Do things I mentioned seem to justify getting a better case and larger powersupply?