How to build a decent gaming PC out of an old computer?

Heres the Computer itself:

HP Pavilion Slimline s3500f PC
Graphics Card: NVIDIA GeForce 6150SE Graphics

Probably only like 1gb- 500MB/ 2GB Ram Left

OS: Windows VIsta 64 bit

And AMD Athlon X2 Dual Core Processor

Basically, I would like to be able to play Minecraft PC and such at 60-100FPS when online.(Currently AVG 15-30FPS.)

So Im curious on what Id need to buy, (Bonus points if price range is under 200$)

If anyone can inform me on what I need and how to install it, I shall award thy 10 points.

Thanks!
Nana

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