Hardware HELP (O-Over DRIIIVE)

[Marshtomp]

(sorry. Listening to that song by Iosys as im posting this :3)

I need some help. I know Nothing about computers and i want to be able to play games such as Team Fortress 2 (Well Smoother anyway) Bioshock and GTA4. But the main reason i want a new processor is so that i can render 3D Animations properly. I don't Have Maya but i work well with Blender and its hard enough modeling with this computer. I was thinking of buying a Dual or Multi Core Processor. But i wanted to know if that is the right thing to do? Should i upgrade the Processor, Ram, Video Card, or Just buy a new computer completely?

Here is the Info on my Computer from Direct X Diag
Some of these i'm Sure don't matter but ill post them anyway.
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Operating System: Windows Vista™ Home Premium (6.0, Build 6001) Service Pack 1 (6001.vistasp1_gdr.080917-1612)
System Manufacturer: Gateway
System Model: D5239
BIOS: Phoenix - Award WorkstationBIOS v6.00PG
Processor: AMD Athlon(tm) 64 Processor 3800+, ~2.4GHz
Memory: 894MB RAM
DirectX Version: DirectX 10

Card name: NVIDIA GeForce 6100 nForce 405
Manufacturer: NVIDIA
Chip type: GeForce 6100 nForce 405

Please Help.. Im a total Noob at computers!