Need some help and advice

Ok so i know that i am a noob because i just started to get into this. So i am running

AMD Athlon(tm) 64 X2 Dual Core Processor 5200+

Memory (RAM) 8.00 GB ddr2 osz

Graphics NVIDIA GeForce 8400 GS

Gaming graphics 1279 MB Total available graphics memory

System type 64-bit operating system

Primary hard disk 113GB Free (233GB Total)

I am not a big gamer yet, but i just want a wicked fast computer ALOT faster than normal. I would rather get comfortable with messing around with over clocking and learning about it first before i start to build another system. I am trying to overclock my computer now in bios but i am not able to turn up the voltage. i currently have it at 3.0 MHz but my temp is still around 42c. The Highest that the voltage goes to is 1.350. Can any one tell me why is it because that is all my motherboard will support tuning wise. Or is it my power supply not strong enough (420 watts). Also does any one have any suggestions cause i want to up grade

I don't play a lot of games yet but i wondering about a good graphics card dual graphic card??

CPU a good one for the future that i can start looking for

Maybe another motherboard one that is good for overclocking

When i get back up to college i am going to start to build a new computer wither it is AMD OR INTEL. I want to replace the computer i have not eventually with nice and fast one that i want to build

Thanks again