Seeking advice on upgrading a computer from 2004

[redskingiant]

I have inherited an old computer from 2004 that was a sweet gaming rig back in the day. It's in a huge alienware case with blue neon lights and skulls and tons of fans.

I HAVE:
Motherboard: ACPI multiproccesor
CPU: Pentium 4 - 3.4ZGHZ, I think two of them, there are two listed in device manager
RAM: 3GB
GPU: nvidia Geforce 6800

My goals are to run Star Wars: The Old Republic, Skyrim, Battlefield 3, Mass Effect 2, GTA 4 and all modern mmos and games. I would like to do this for $300-400

I WANT:
GPU I'm considering:
Zotac gts 450 - $100 newegg
Sapphire Radeon HD 6870 - $160
Geforce GTX 560 $190-220

CPU:
Intel Core i3-2100 Sandy Bridge 3.1GHz -$130
Intel Core i5-2400 Sandy Bridge 3.1GHz - $190
Intel Core i5-2500K Sandy Bridge 3.3GHz -$220

Memory
Kingston HyperX T1 Series 8GB (2 x 4GB) 240-Pin - $80

So is the difference between CPUs and GPUs big enough to justify spending $500 for GTX 560 and i5 or spend $310 for GTS 450 and i3? Also do I need to upgrade my motherboard?


Should i consider upgrading from XP to windows 7, will that effect speed for gaming?

I am a complete noob to building computers and know there is something about matching pins and stuff and would hate to buy something for it not to fit, how do i check this?

Thanks so much for your time I am a total noob and really need advice

 

[r0aringdrag0n]

Hi! First, if you are to upgrade the CPU, then you HAVE TO upgrade the Motherboard as the Pentium series MoBo's are NOT compatible with the 2nd gen intel CPUs. I would recommend you get the core i5 2500k as this will allow you to play games further into the future because it has 4 cores, instead of the 2 in the i3. If you want a cheaper upgrade, you can go with 4GB of RAM instead of 8, 8 is overkill right now and when you need more, you can easily buy more. For the graphics card, I suggest the gtx 560 or the Radeon 6950.
As fir the Windows, you don't need to upgrade until later, where the games will not support Windows xp as an OS